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Water Distribution Operator Class I study materials
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Water Distribution Operator Class I practice questions

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Question 1Water Sources, Supply, and System Layout

Water that fills the pore spaces of soil and rock below the water table is called:

  1. Surface water
  2. Perched water
  3. Capillary water
  4. Groundwater Correct answer.

Explanation

Groundwater is the water stored in and moving through the saturated pores and fractures of soil and rock beneath the water table. Surface water is found in streams, lakes, and reservoirs, while perched and capillary water are localized or unsaturated-zone occurrences.

Question 2Water Sources, Supply, and System Layout

An aquifer that is bounded above by a confining layer and whose water is under pressure is called:

  1. A confined aquifer Correct answer.
  2. A perched aquifer
  3. An unconfined aquifer
  4. An alluvial aquifer

Explanation

A confined aquifer is overlain by a relatively impermeable confining layer, so its water is under pressure and can rise above the top of the aquifer in a well. An unconfined aquifer has a water table exposed to atmospheric pressure, and a perched aquifer is a small localized saturated zone above the main water table.

Question 3Water Sources, Supply, and System Layout

Which distribution system layout consists of a network of intersecting pipes that lets water reach a point by more than one path?

  1. Radial system
  2. Tree system
  3. Dead-end system
  4. Grid system Correct answer.

Explanation

A grid, or looped, system connects mains so that water can travel to most points by more than one route, which improves reliability and reduces stagnant dead ends. Dead-end and tree systems rely on single paths, and a radial system feeds outward from one central point.

Question 4Water Sources, Supply, and System Layout

Which function does an elevated storage tank primarily serve in a distribution system?

  1. Equalizing pressure and demand Correct answer.
  2. Removing dissolved gases from water
  3. Adding fluoride to the supply
  4. Filtering suspended solids out

Explanation

Elevated storage uses gravity to maintain pressure and supplies extra water during peak demand or emergencies while refilling during low-demand periods. Treatment functions such as gas removal, filtration, and fluoridation are performed at treatment facilities, not by the storage tank.

Question 5Water Sources, Supply, and System Layout

The water table is best described as:

  1. The elevation of the land surface
  2. The top of the confining layer
  3. The base of the well screen
  4. The top of the saturated zone Correct answer.

Explanation

The water table is the upper boundary of the saturated zone, where pore water pressure equals atmospheric pressure. It is not the land surface, the well screen, or the top of a confining layer.

Question 6Water Sources, Supply, and System Layout

A wellhead protection area is established primarily to:

  1. Allow a higher well pumping rate
  2. Reduce the cost of drilling the well
  3. Improve the taste of the well water
  4. Protect the well from contamination Correct answer.

Explanation

A wellhead protection area is the land surface and subsurface zone through which contaminants could reach a public water-supply well. Managing activities in that area helps prevent contamination from entering the well and its recharge zone.

Question 7Water Sources, Supply, and System Layout

A river intake should generally be located:

  1. Immediately downstream of a wastewater outfall
  2. At the point of highest current velocity
  3. In a shallow area close to the river bank
  4. Where the water is deepest and flow is stable Correct answer.

Explanation

A river intake is best placed in deep, stable-flow water where it is protected from bed load, debris, and low-flow exposure. Locations with very high velocity, shallow depth, or nearby contamination sources increase operating and water-quality problems.

Question 8Water Sources, Supply, and System Layout

Pressure zones in a distribution system are used mainly to:

  1. Reduce the number of system valves
  2. Increase the chlorine demand of the water
  3. Keep pressures adequate across elevations Correct answer.
  4. Eliminate the need for storage tanks

Explanation

Because pressure increases with depth and elevation differences, a large system is divided into pressure zones so that each area receives an acceptable pressure range. Valves or pressure-reducing stations separate the zones, and storage and pumping are matched to each zone.

Question 9Water Sources, Supply, and System Layout

The hydraulic grade line in a distribution system represents:

  1. The physical elevation of the pipe centerline
  2. The pressure in psi multiplied by pipe diameter
  3. The maximum flow velocity in the main
  4. The height water would reach in an open tube Correct answer.

Explanation

The hydraulic grade line is the elevation to which water would rise in an open piezometer connected to the pipe, combining pressure head and elevation head. It is not simply the pipe elevation, a pressure-times-diameter product, or a velocity value.

Question 10Water Sources, Supply, and System Layout

The cone of depression around a pumping well is caused by:

  1. Artesian pressure rising above the well
  2. Drawdown of the water table at the well Correct answer.
  3. Backflow from the distribution system
  4. A leak in the well casing below ground

Explanation

Pumping lowers the water level near the well, creating a roughly conical depression in the water table or potentiometric surface that extends outward from the well. The effect is a normal result of drawdown, not a casing leak or backflow condition.

Question 11Water Sources, Supply, and System Layout

Fire flow requirements in a distribution system are most influenced by:

  1. Building size, construction, and use Correct answer.
  2. The total length of the transmission main
  3. The number of service connections
  4. The elevation of the storage tank

Explanation

Fire flow is the rate and duration of water needed to suppress a fire, so it depends mainly on the size, construction, occupancy, and exposure of the buildings being protected. Service connection counts, tank elevation, and main length affect system performance but are not the primary basis for the fire flow requirement.

Question 12Water Sources, Supply, and System Layout

Isolation valves in a distribution system are installed mainly to:

  1. Prevent any cross-connection
  2. Isolate mains for repairs Correct answer.
  3. Measure flow through the main
  4. Release trapped air pockets

Explanation

Isolation valves let operators shut down a section of main so repairs or maintenance can be done without interrupting service to the entire system. Flow measurement, air release, and cross-connection control are handled by other devices and programs.

Question 13Water Sources, Supply, and System Layout

The land area that drains to a particular river or reservoir is called a:

  1. Watershed Correct answer.
  2. Catch basin
  3. Floodplain
  4. Aquifer

Explanation

A watershed is the drainage area from which runoff flows to a common river, lake, or reservoir. An aquifer is a groundwater formation, a floodplain is land beside a watercourse, and a catch basin is a drainage structure.

Question 14Water Sources, Supply, and System Layout

Which practice best protects a surface water supply watershed?

  1. Removing vegetation along the streams
  2. Controlling erosion and limiting development Correct answer.
  3. Discharging treated sewage upstream
  4. Increasing fertilizer use near the reservoir

Explanation

Erosion control and careful management of development reduce sediment and pollutant loading to streams and reservoirs. Fertilizer use, upstream sewage discharges, and removal of streamside vegetation all tend to degrade source water quality.

Question 15Water Sources, Supply, and System Layout

Transmission mains differ from distribution mains in that transmission mains:

  1. Carry large flows between major facilities Correct answer.
  2. Serve individual customer service lines directly
  3. Are always smaller in diameter than distribution mains
  4. Are used only for fire protection

Explanation

Transmission mains move large quantities of water from sources, treatment plants, or storage facilities to the distribution system. Distribution mains serve customer connections and hydrants, and they are typically smaller than transmission mains.

Question 16Water Sources, Supply, and System Layout

A storage tank water surface is 100 ft above a service connection, where the static pressure is about 43 psi. If the tank water level drops 30 ft, the pressure at that connection becomes about:

  1. About 43 psi
  2. About 30 psi Correct answer.
  3. About 26 psi
  4. About 13 psi

Explanation

Static pressure from elevation is approximately 0.433 psi per foot of head. After a 30 ft drop, the remaining head is 70 ft, and 70 ft times 0.433 psi/ft equals about 30 psi.

Question 17Distribution System Components, Materials, and Design

Which service line material is commonly joined with solder or compression fittings and is chosen for its long service life in small-diameter lines?

  1. Asbestos-cement pipe
  2. Steel pipe with cement lining
  3. Ductile iron pipe
  4. Copper tubing Correct answer.

Explanation

Copper tubing is joined by soldering or compression fittings and is widely used for small service lines because it resists corrosion and lasts a long time. Ductile iron and steel pressure pipe are joined by push-on or mechanical joints, and asbestos-cement is not used for interior service connections.

Question 18Distribution System Components, Materials, and Design

Gate valves are widely used in distribution systems because they:

  1. Throttle flow smoothly and precisely across the full range of travel
  2. Vent trapped air from high points
  3. Isolate sections with low head loss when fully open Correct answer.
  4. Prevent reverse flow automatically

Explanation

A gate valve's gate retracts fully out of the waterway, so a wide-open gate valve adds very little head loss and is well suited to isolating sections of main. Gate valves are not intended for throttling, and they do not prevent backflow or release air.

Question 19Distribution System Components, Materials, and Design

Which valve permits flow in one direction only and closes automatically when flow reverses?

  1. Pressure reducing valve
  2. Air release valve
  3. Check valve Correct answer.
  4. Butterfly valve

Explanation

A check valve opens with forward flow and seats shut when flow stops or reverses, protecting pumps and preventing backflow. Butterfly valves are isolating valves, pressure reducing valves control downstream pressure, and air release valves vent air.

Question 20Distribution System Components, Materials, and Design

Small-diameter PVC water pipe is most commonly assembled using which joining method?

  1. Flanged connections with gaskets and bolts
  2. Heat fusion of the pipe ends
  3. Lead caulking and jute
  4. Primer and solvent cement Correct answer.

Explanation

PVC joints are made by cleaning and priming the bell and spigot, then applying solvent cement, which softens the surfaces so they fuse together. Heat fusion is used for polyethylene, lead caulking for older cast iron, and flanges only at special connections.

Question 21Distribution System Components, Materials, and Design

Thrust blocks are installed at bends, tees, and dead ends to:

  1. Prevent the pipe from floating during backfill
  2. Resist the longitudinal force created when flow changes direction Correct answer.
  3. Provide electrical grounding for the main
  4. Protect the pipe from frost heave

Explanation

Internal pressure acting on a bend or tee produces a resultant force that tries to push the pipe apart at the joints. A thrust block transfers that force into undisturbed soil so the joints are not pulled apart. Flotation, frost heave, and grounding are handled by other means.

Question 22Distribution System Components, Materials, and Design

Which fitting joins two pipes of different diameters?

  1. Tee
  2. Cap
  3. Elbow
  4. Reducer Correct answer.

Explanation

A reducer makes the transition between two different pipe sizes. A cap closes a pipe end, a tee makes a branch connection, and an elbow changes the direction of the line.

Question 23Distribution System Components, Materials, and Design

Why is the depth of cover for a water main specified relative to the local frost line?

  1. To reduce pumping energy costs
  2. To keep the water cool during summer months
  3. To allow gravity flow to every customer
  4. To prevent water in the main from freezing Correct answer.

Explanation

Burying the main below the frost line keeps the soil around it from freezing, so the water in the pipe does not freeze and interrupt service. Depth of cover also protects the pipe from traffic loads, but frost protection is the reason it is tied to the frost line.

Question 24Distribution System Components, Materials, and Design

Which device records the volume of water delivered to an individual customer?

  1. Water meter Correct answer.
  2. Pressure reducing valve
  3. Backflow preventer
  4. Blowoff

Explanation

A water meter measures and totalizes the volume passing through a service line so the customer can be billed. Pressure reducing valves control pressure, backflow preventers protect the public supply, and blowoffs flush mains.

Question 25Distribution System Components, Materials, and Design

A 12-inch main must be installed in a cramped vault and opened or closed quickly during an emergency. Which valve best fits these conditions?

  1. Swing check valve
  2. Gate valve
  3. Butterfly valve Correct answer.
  4. Globe valve

Explanation

A butterfly valve is compact, requires only a quarter turn to operate, and fits well in tight spaces. Gate valves need much more vertical clearance for the stem and handwheel travel, globe valves have high head loss, and check valves cannot be used for isolating flow.

Question 26Distribution System Components, Materials, and Design

Air release valves are installed at high points of a main in order to:

  1. Vent accumulated air that would otherwise restrict flow Correct answer.
  2. Stop surges from reaching the pump station
  3. Drain accumulated sediment from low points
  4. Measure line pressure at the highest elevation

Explanation

Air collects at high points and can reduce capacity, cause erratic metering, and contribute to surge. Air release valves vent that trapped air automatically while the main is under pressure. Sediment removal is the job of blowoffs at low points and dead ends.

Question 27Distribution System Components, Materials, and Design

A long dead-end main collects sediment and stale water. Which appurtenance is installed at the end of the main to flush it?

  1. Blowoff Correct answer.
  2. Corporation stop
  3. Pressure reducing valve
  4. Air release valve

Explanation

A blowoff at a low point or dead end allows operators to open the line and flush out sediment and stagnant water. Air release valves handle air at high points, pressure reducing valves control pressure, and corporation stops tap service lines.

Question 28Distribution System Components, Materials, and Design

A thrust block cannot be used at a bend on a PVC main because the trench is congested with other utilities. What is the appropriate alternative?

  1. Lead caulking the bell and spigot
  2. Using a mechanical restraint joint with a locking gland Correct answer.
  3. Welding the joint
  4. Installing a flexible coupling at the bend

Explanation

Mechanical restraint joints use gripping devices and a locking gland to transfer thrust across the joint, so no external block is needed. PVC cannot be welded or lead caulked, and a flexible coupling does not resist thrust.

Question 29Distribution System Components, Materials, and Design

A cement mortar lining applied to the inside of a ductile iron main serves to:

  1. Make the pipe easier to tap under pressure
  2. Increase the pipe's external load capacity
  3. Protect the metal from corrosion and tuberculation Correct answer.
  4. Allow the use of solvent cement joints

Explanation

The mortar lining creates an alkaline barrier at the pipe wall that inhibits corrosion and prevents tuberculation, which would otherwise raise friction losses. It does not add structural strength, aid tapping, or change how joints are made.

Question 30Distribution System Components, Materials, and Design

Which device provides the highest degree of protection against backflow into a public water supply?

  1. An air gap Correct answer.
  2. An atmospheric vacuum breaker
  3. A double check valve assembly
  4. A reduced pressure principle assembly

Explanation

An air gap physically separates the potable supply from the receiving vessel, so backflow is impossible even under backpressure or backsiphonage. Mechanical assemblies such as RP devices, double check valves, and vacuum breakers rely on components that can fail or be bypassed.

Question 31Distribution System Components, Materials, and Design

A corporation stop is used to:

  1. Tap a service line into a live main Correct answer.
  2. Measure flow at a fire hydrant
  3. Release air from a high point
  4. Isolate a section of main for repair work

Explanation

A corporation stop is screwed directly into a tapped main and is the first valve on a service line, allowing the connection to be made without shutting down the main. Section isolation is done with gate or butterfly valves.

Question 32Distribution System Components, Materials, and Design

Properly placed and compacted bedding under and beside a flexible pipe is important because it:

  1. Reduces the chlorine demand of the water
  2. Increases the pipe's internal pressure rating
  3. Prevents corrosion of the pipe wall
  4. Supports the pipe and limits deflection under load Correct answer.

Explanation

A flexible pipe relies on the soil envelope at its sides and haunches to carry load, so proper bedding limits ovaling and deflection. Bedding has no effect on pressure rating, corrosion, or water quality.

Question 33Distribution System Components, Materials, and Design

A steel casing pipe is installed where a water main crosses beneath a highway primarily to:

  1. Provide a location for a meter
  2. Increase the flow capacity of the crossing
  3. Allow the main to drain by gravity
  4. Carry the main and shield it from external loads Correct answer.

Explanation

A casing carries the carrier pipe through the crossing and takes the traffic loads so the water main is not damaged and the roadway does not have to be excavated for repairs. It does not change flow capacity or provide metering.

Question 34Distribution System Components, Materials, and Design

Valve boxes are installed over buried valves in order to:

  1. Provide access to the operating nut and keep out debris Correct answer.
  2. Prevent the valve from freezing in winter
  3. Support the weight of the pipe above the valve
  4. Measure the valve position electrically

Explanation

A valve box extends from the valve operating nut to the ground surface so crews can reach the nut with a key and operate the valve, while keeping soil and debris off the mechanism. It is not a freeze protection or structural device.

Question 35Distribution System Components, Materials, and Design

A centrifugal pump drawing suction from a storage tank whose water surface is below the pump must:

  1. Be primed so the pump casing is full of water Correct answer.
  2. Have a check valve on the suction side
  3. Be a positive displacement type
  4. Operate with the discharge valve closed for long periods

Explanation

A centrifugal pump cannot pump air, so when it sits above the water surface it must be primed to fill the casing and suction line before starting. Check valves belong on the discharge side, and running against a closed discharge for long periods overheats the pump.

Question 36Distribution System Components, Materials, and Design

An elevated storage tank maintains pressure in the distribution system by means of:

  1. Compressed air maintained in the tank
  2. The elevation head of the water surface Correct answer.
  3. A booster pump mounted inside the tank
  4. Reduced friction loss in the connecting main

Explanation

Pressure at any point equals the height of the water surface above that point, so an elevated tank sets the hydraulic grade line for the area it serves. It uses gravity, not air pressure or built-in pumps, to provide that pressure.

Question 37Distribution System Components, Materials, and Design

A pump discharging into a long main has a check valve that slams shut when the pump stops. Which measure best reduces the resulting pressure surge?

  1. Reduce the diameter of the discharge main
  2. Increase pump speed so the check valve stays open longer
  3. Replace the check valve with a gate valve left fully open
  4. Install a surge relief valve or air vessel near the pump discharge Correct answer.

Explanation

Surge magnitude depends on how fast the flow velocity changes, so absorbing or relieving the pressure wave near its source limits the rise. A surge relief valve, air vessel, or flywheel effect slows the velocity change and protects the main.

Question 38Distribution System Components, Materials, and Design

Two 8-inch mains of equal length carry the same flow. Main A is unlined cast iron with C = 100; Main B is cement-mortar-lined ductile iron with C = 130. Which statement is correct?

  1. Head loss is the same because both mains have the same diameter
  2. Main A has less head loss; a lower C means less friction
  3. Main B has less head loss; a higher C means a smoother interior Correct answer.
  4. Head loss depends only on flow rate and not on the C value

Explanation

In the Hazen-Williams equation, head loss is inversely proportional to C raised to about the 1.85 power, so the higher the C, the lower the friction loss for the same flow and diameter. The smoother lined pipe therefore loses less head.

Question 39Distribution System Components, Materials, and Design

Thrust at a bend depends on internal pressure, pipe cross-sectional area, and bend angle. Which single change would most increase the thrust force at an existing 45-degree bend?

  1. Replacing the pipe with one size larger
  2. Reducing the bend angle from 45 degrees to 22.5 degrees
  3. Doubling the flow velocity through the bend
  4. Doubling the operating pressure in the main Correct answer.

Explanation

Thrust equals 2 times pressure times area times the sine of half the bend angle, so it scales directly with pressure; doubling pressure doubles the thrust. Velocity contributes only a small momentum component, and a smaller bend angle or one size increase changes the force by less than a factor of two.

Question 40Distribution System Components, Materials, and Design

Water flushed from a newly chlorinated main is commonly dechlorinated before discharge because:

  1. The water will raise the pH of the receiving stream above drinking water standards
  2. Chlorine will corrode the inside of storm sewer pipe
  3. Chlorine at high concentrations is toxic to fish and aquatic life Correct answer.
  4. Residual chlorine will freeze in cold weather

Explanation

The strong chlorine solution used to disinfect new mains can harm fish and other aquatic organisms if discharged directly, so it is neutralized before release. The concern is toxicity to the receiving water, not pipe corrosion or pH.

Question 41Distribution System Components, Materials, and Design

A new subdivision is served by a single 3,000-foot, 8-inch main with no connection at the far end. What is the main operational concern with this arrangement?

  1. Inability to install fire hydrants along the main
  2. Increased thrust at the fittings along the main
  3. Excessive flow velocity during peak demand
  4. Loss of chlorine residual and sediment buildup from stagnation Correct answer.

Explanation

Long dead ends leave water sitting in the pipe for extended periods, which depletes disinfectant residual and allows sediment to settle, and there is no alternate path if the main fails. Looping the main would restore circulation and reliability.

Question 42Distribution System Components, Materials, and Design

Which pipe material is lightweight, flexible, and naturally resistant to corrosion, making it common for small-diameter distribution mains?

  1. Ductile iron
  2. Galvanized steel
  3. PVC Correct answer.
  4. Asbestos-cement

Explanation

PVC pipe is lightweight, flexible, and does not corrode in the way metallic pipe does, so it is widely used for small-diameter water mains. Ductile iron is strong but requires lining and coating for corrosion protection. Asbestos-cement is rigid and brittle, and galvanized steel is susceptible to corrosion.

Question 43Distribution System Components, Materials, and Design

After a fire hydrant is closed, the drain valve at the bottom of the barrel serves to:

  1. prevent backflow into the main
  2. relieve pressure surges in the main
  3. drain the barrel to the ground Correct answer.
  4. measure flow during flushing

Explanation

When the hydrant main valve is closed, the drain valve opens and lets water left in the barrel drain into the ground. This helps prevent the barrel from holding water that could freeze and damage the hydrant. The drain valve does not control main pressure, measure flow, or provide backflow protection.

Question 44Distribution System Components, Materials, and Design

Which valve type is designed primarily for throttling service and has relatively high head loss when fully open?

  1. Gate
  2. Butterfly
  3. Check
  4. Globe Correct answer.

Explanation

A globe valve uses a plug and seat arrangement that forces flow through a tortuous path, which makes it well suited to throttling and regulating flow. That same flow path produces relatively high head loss even when the valve is fully open. Gate valves are intended for fully open or fully closed service, and check valves allow flow in only one direction.

Question 45Distribution System Components, Materials, and Design

A ductile iron main is to be installed in soil known to be corrosive. Which method is commonly used to protect the pipe's exterior?

  1. Increased flow velocity
  2. Polyethylene wrap Correct answer.
  3. Interior epoxy coating
  4. Cement mortar lining

Explanation

Polyethylene wrap or encasement is commonly placed around ductile iron pipe to separate the metal from aggressive soil and reduce external corrosion. Cement mortar lining and interior epoxy coating protect the inside of the pipe, not the outside. Increasing flow velocity does not protect the pipe exterior and can increase internal wear and head loss.

Question 46Distribution System Components, Materials, and Design

A distribution main must deliver 1,500 gpm at a velocity no greater than 5 ft/s. What is the smallest nominal pipe diameter that satisfies this limit?

  1. 14-inch
  2. 10-inch
  3. 8-inch
  4. 12-inch Correct answer.

Explanation

First convert 1,500 gpm to about 3.34 cubic feet per second. At 5 ft/s the required cross-sectional area is 3.34 divided by 5, or about 0.668 square feet, which corresponds to a diameter of about 11.1 inches. The smallest standard nominal size that keeps velocity at or below 5 ft/s is therefore 12-inch.

Question 47Pipe Installation, Repair, and Maintenance

What is the main purpose of placing bedding material beneath and alongside a newly laid water main?

  1. To keep the pipe from rolling during backfilling operations
  2. To raise the pipe above the water table in the trench
  3. To bond the pipe to the surrounding soil for restraint
  4. To support the pipe evenly and spread loads Correct answer.

Explanation

Bedding gives the pipe uniform support along its barrel and distributes surface loads into the surrounding soil. Point loading from rocks or a hard, uneven trench bottom can crack the pipe or damage its coating.

Question 48Pipe Installation, Repair, and Maintenance

A newly installed water main is pressure tested at the specified test pressure for a minimum duration of:

  1. 12 hours
  2. 10 minutes
  3. 24 hours
  4. 2 hours Correct answer.

Explanation

Standard practice for acceptance testing of a new main is to hold the test pressure for at least two hours while makeup water is measured. The test pressure itself is typically 1.5 times the working pressure, with a minimum value set by the specification.

Question 49Pipe Installation, Repair, and Maintenance

A thrust block installed at a bend in a water main is designed primarily to:

  1. Absorb the pressure surges that travel through the pipeline
  2. Provide a corrosion barrier that protects the joint from soil attack
  3. Anchor the pipe barrel firmly to the trench bottom during backfill
  4. Resist the unbalanced thrust caused by the change in direction Correct answer.

Explanation

Whenever flow changes direction at a bend or tee, internal pressure produces an unbalanced thrust that tries to push the fitting off the line. A thrust block transmits that force into undisturbed soil.

Question 50Pipe Installation, Repair, and Maintenance

Which fitting develops the greatest hydraulic thrust and therefore needs the most restraint?

  1. A 22.5-degree bend
  2. A 90-degree bend Correct answer.
  3. A 45-degree bend
  4. A straight run of pipe

Explanation

Thrust grows as the angle of deflection increases, because the change in direction of the momentum and pressure forces is larger. A 90-degree bend therefore produces considerably more thrust than a 45-degree or 22.5-degree bend, and a straight run produces none.