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NRPP RMP practice questions

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Question 1Radon Measurement Fundamentals and Physics

Radon-222 decays into which element, marking the start of the short-lived decay chain commonly measured in homes?

  1. Lead-214
  2. Bismuth-214
  3. Polonium-218 Correct answer.
  4. Radium-226

Explanation

Radon-222 undergoes alpha decay to polonium-218, which begins the short-lived progeny chain. Radium-226 is the parent of radon, and lead-214 and bismuth-214 occur later in the chain.

Question 2Radon Measurement Fundamentals and Physics

What is the half-life of radon-222?

  1. 3.8 hours
  2. 1600 years
  3. 22 years
  4. 3.8 days Correct answer.

Explanation

Radon-222 has a half-life of about 3.8 days, which allows it to accumulate indoors while decaying relatively quickly. The other values correspond to other radionuclides or are simply incorrect.

Question 3Radon Measurement Fundamentals and Physics

Radon-222 is a gas because it belongs to which group of elements on the periodic table?

  1. Halogens
  2. Alkaline earth metals
  3. Alkali metals
  4. Noble gases Correct answer.

Explanation

Radon is a noble gas, which explains its chemical inertness and its ability to migrate as a gas. Its Group 18 position is why it does not readily form compounds in indoor air.

Question 4Radon Measurement Fundamentals and Physics

Which type of radiation is emitted when radon-222 decays to polonium-218?

  1. Neutron
  2. Beta particle
  3. Gamma ray
  4. Alpha particle Correct answer.

Explanation

Radon-222 loses two protons and two neutrons, emitting an alpha particle to become polonium-218. Alpha emission reduces the mass number by four and the atomic number by two.

Question 5Radon Measurement Fundamentals and Physics

What are the standard units used to report radon concentration in the United States?

  1. Picocuries per liter (pCi/L) Correct answer.
  2. Grams per cubic meter (g/m3)
  3. Becquerels per cubic meter (Bq/m3)
  4. Millisieverts per year (mSv/yr)

Explanation

US practice reports radon gas concentration in picocuries per liter, where one picocurie equals 2.22 decays per minute. Bq/m3 is the SI unit used elsewhere, and mSv/yr expresses dose rather than concentration.

Question 6Radon Measurement Fundamentals and Physics

One picocurie per liter (pCi/L) is equivalent to how many becquerels per cubic meter (Bq/m3)?

  1. 3.7
  2. 370
  3. 0.037
  4. 37 Correct answer.

Explanation

The conversion factor is 1 pCi/L equals 37 Bq/m3, derived from 1 pCi = 0.037 Bq and 1 L = 0.001 m3. This factor is used whenever US and SI concentrations must be compared.

Question 7Radon Measurement Fundamentals and Physics

Which radon decay progeny is primarily responsible for delivering the alpha dose to lung tissue?

  1. Polonium-218 and polonium-214 Correct answer.
  2. Radon-222 itself
  3. Bismuth-210
  4. Lead-210

Explanation

The short-lived alpha emitters polonium-218 and polonium-214 attach to airborne particles that deposit in the lung. Radon gas is inhaled and mostly exhaled, so its progeny carry most of the alpha dose.

Question 8Radon Measurement Fundamentals and Physics

Which instrument measures radon by counting alpha particles from decay products collected on a filter after air is drawn through it?

  1. Continuous radon monitor
  2. Working level meter using grab sampling Correct answer.
  3. Charcoal canister
  4. Alpha track detector

Explanation

Grab-sampling working level devices pull air through a filter and measure alpha activity from collected progeny. Charcoal canisters and alpha track detectors integrate over time, and continuous monitors sample the detector chamber over defined intervals.

Question 9Radon Measurement Fundamentals and Physics

A radon measurement result of 148 Bq/m3 is approximately equal to which concentration in pCi/L?

  1. 14.8 pCi/L
  2. 0.25 pCi/L
  3. 4.0 pCi/L Correct answer.
  4. 40 pCi/L

Explanation

Dividing 148 Bq/m3 by the conversion factor of 37 Bq/m3 per pCi/L gives about 4.0 pCi/L. This concentration aligns with the common US action level.

Question 10Radon Measurement Fundamentals and Physics

If a radon sample begins with an activity of 8.0 pCi/L, what activity remains after 7.6 days, assuming only radioactive decay?

  1. 1.0 pCi/L
  2. 4.0 pCi/L
  3. 2.0 pCi/L Correct answer.
  4. 0.5 pCi/L

Explanation

A half-life of about 3.8 days means 7.6 days equals two half-lives, so the activity is quartered. One quarter of 8.0 pCi/L is 2.0 pCi/L.

Question 11Radon Measurement Fundamentals and Physics

Why does radon concentration in a basement often show a diurnal pattern, higher at night than in the afternoon?

  1. Indoor-outdoor temperature differences drive the stack effect and change ventilation Correct answer.
  2. Soil radium content increases after sunset
  3. Radon decay rate increases in cooler nighttime air
  4. Outdoor radon levels peak at night and diffuse indoors

Explanation

At night the indoor-outdoor temperature difference strengthens the stack effect, drawing more soil gas indoors while ventilation is reduced. The decay rate and soil radium content do not change with time of day.

Question 12Radon Measurement Fundamentals and Physics

Which statement best describes the relationship between radon gas and its short-lived progeny in indoor air?

  1. Progeny are chemically identical to radon gas
  2. Progeny concentrations always equal gas concentrations
  3. Progeny exist as charged or unattached particles that plate out or attach to aerosols Correct answer.
  4. Progeny are stable and do not decay indoors

Explanation

Short-lived progeny are metals that form ions or ultrafine particles, which either attach to airborne aerosols or plate out on surfaces. Their behavior differs from the inert radon gas, so gas and progeny concentrations are not equal.

Question 13Radon Measurement Fundamentals and Physics

A closed-house condition is required before and during a short-term radon test primarily to do what?

  1. Standardize the ventilation state so results are comparable Correct answer.
  2. Allow the soil to recharge its radon supply
  3. Ensure the detector stays below its saturation limit
  4. Prevent indoor radon from escaping through open windows

Explanation

Closed-house conditions standardize ventilation so results reflect typical occupied conditions and are comparable between tests. It is not intended to prevent escape or to recharge soil gas.

Question 14Radon Measurement Fundamentals and Physics

Which of the following is an integrating measurement device that records radon exposure over a period of weeks to months?

  1. Continuous monitor reporting hourly values
  2. Electret ion chamber used for a 48-hour test
  3. Alpha track detector Correct answer.
  4. Scintillation cell grab sampler

Explanation

Alpha track detectors accumulate damage tracks from alpha decays over long exposures, making them long-term integrating devices. The other devices provide short-term or grab measurements.

Question 15Radon Measurement Fundamentals and Physics

Radon-222 is produced in soil primarily from the decay of which parent nuclide?

  1. Potassium-40
  2. Thorium-232
  3. Radium-226 Correct answer.
  4. Uranium-238

Explanation

Radium-226, part of the uranium-238 series, decays directly into radon-222. Uranium-238 is the series head and thorium-232 leads a different series producing radon-220.

Question 16Radon Measurement Fundamentals and Physics

A short-term radon test result is 3.9 pCi/L. What is the most appropriate interpretation under typical US guidance?

  1. Immediate mitigation is required
  2. Confirm with a follow-up test since it is near the action level Correct answer.
  3. No action is needed because it is below 4 pCi/L
  4. The result indicates a measurement error

Explanation

Results near the 4 pCi/L action level warrant confirmation with a follow-up test, especially for short-term measurements. Immediate mitigation is generally reserved for clearly elevated confirmed results.

Question 17Radon Measurement Fundamentals and Physics

Why is radon-220 (thoron) generally of less concern than radon-222 in indoor air measurements?

  1. It cannot enter buildings through soil
  2. Its much shorter half-life limits accumulation and transport Correct answer.
  3. It is chemically reactive and breaks down indoors
  4. It does not emit alpha particles

Explanation

Radon-220 has a half-life of about 55 seconds, so it decays before migrating far from its source and rarely accumulates indoors. It still emits alpha radiation and enters through the same pathways.

Question 18Radon Measurement Fundamentals and Physics

What does a working level (WL) quantify?

  1. Radon gas concentration in picocuries per liter
  2. The detector's lower limit of detection
  3. The potential alpha energy concentration of short-lived progeny Correct answer.
  4. The annual effective dose in millisieverts

Explanation

One working level represents the potential alpha energy concentration from short-lived progeny equivalent to 1.3e5 MeV per liter of air. It describes progeny energy, not gas concentration or dose directly.

Question 19Radon Measurement Fundamentals and Physics

A detector's calibration is checked and found to read 10 percent high. If it reports 5.5 pCi/L, what is the corrected concentration?

  1. 5.4 pCi/L
  2. 5.0 pCi/L Correct answer.
  3. 6.1 pCi/L
  4. 4.5 pCi/L

Explanation

If the device reads 10 percent high, the corrected value is the reading divided by 1.10, giving 5.0 pCi/L. Multiplying by 1.10 would incorrectly amplify the bias.

Question 20Radon Measurement Fundamentals and Physics

Which factor most directly increases the entry of soil gas into a house?

  1. A larger yard area
  2. Higher outdoor humidity
  3. Brighter indoor lighting
  4. A pressure difference drawing soil gas toward the foundation Correct answer.

Explanation

Pressure-driven flow, caused by the stack effect or exhaust appliances, draws soil gas through foundation openings. Humidity, lighting, and yard size do not drive soil gas entry.

Question 21Radon Measurement Fundamentals and Physics

A measurement reports 0.02 WL of progeny. Using the common conversion that 1 WL corresponds to about 200 pCi/L of radon at equilibrium (50 percent), what equilibrium-equivalent radon concentration does this roughly represent?

  1. 2 pCi/L
  2. 1 pCi/L
  3. 4 pCi/L Correct answer.
  4. 0.4 pCi/L

Explanation

At 50 percent equilibrium, 1 WL corresponds to roughly 200 pCi/L of radon gas, so 0.02 WL is about 4 pCi/L. This equilibrium-equivalent value allows comparison with gas measurements.

Question 22Radon Measurement Fundamentals and Physics

Why can two homes with identical soil radium content have very different indoor radon concentrations?

  1. Half-life varies with elevation
  2. Detector calibration differs between homes
  3. Radium content is the only variable that matters
  4. Differences in foundation openings, pressure-driven flow, and air exchange alter entry and dilution Correct answer.

Explanation

Indoor radon depends on entry pathways, pressure-driven soil gas flow, and ventilation dilution as well as source strength. Identical soil radium can therefore yield very different indoor concentrations.

Question 23Radon Measurement Fundamentals and Physics

An alpha track detector is exposed for 90 days. Which combination of conditions best supports a valid long-term result?

  1. Detector placed in a closed house with normal occupancy over the full period Correct answer.
  2. Detector moved weekly between floors
  3. Detector placed in a sealed plastic bag during exposure
  4. Detector placed outdoors near the foundation

Explanation

Long-term tests require the detector to remain in place under normal closed-house occupancy for the entire period so the integrated exposure represents typical conditions. Moving, sealing, or placing the detector outdoors invalidates the result.

Question 24Radon Measurement Fundamentals and Physics

Which statement about the relationship between radon gas concentration and progeny equilibrium ratio is correct?

  1. The ratio increases as ventilation increases
  2. The ratio is determined only by the radon half-life
  3. The ratio depends on ventilation and plate-out and can range widely Correct answer.
  4. The equilibrium ratio is fixed at 1.0 in all homes

Explanation

The equilibrium ratio reflects the balance between progeny production and loss through decay, ventilation, and plate-out, so it varies between environments. It is not fixed and does not rise with increased ventilation.

Question 25Radon Measurement Fundamentals and Physics

A continuous monitor reports a sudden spike in apparent radon during the first hours after placement in a home. Which explanation is most consistent with measurement physics?

  1. Outdoor radon permanently entered the home
  2. The detector is equilibrating with ambient conditions and progeny buildup in its chamber Correct answer.
  3. The radon half-life temporarily shortened
  4. Soil radium content increased abruptly

Explanation

Continuous monitors can show transient responses as the detection chamber equilibrates and progeny build up after placement. Half-life and soil radium content do not change abruptly, and outdoor entry would not be permanent.

Question 26Radon Measurement Fundamentals and Physics

Which property of radon-222 allows it to move readily from soil into the indoor environment?

  1. It is a solid metal that sublimates at room temperature.
  2. It is a noble gas with a half-life of about 3.8 days. Correct answer.
  3. It is a chemically reactive gas that binds to soil particles.
  4. It is highly soluble in water and travels only as a dissolved ion.

Explanation

Radon-222 is a noble gas, so it does not react chemically and can migrate through soil pores. Its 3.8-day half-life is long enough to allow movement from soil into buildings.

Question 27Radon Measurement Fundamentals and Physics

What is the primary source of indoor radon in most homes?

  1. Soil gas entering through foundation openings and cracks Correct answer.
  2. Ambient outdoor air infiltrating through windows and doors
  3. Radon dissolved in the public water supply
  4. Off-gassing from building materials such as concrete and drywall

Explanation

In most homes, soil gas is the dominant source of indoor radon. Building materials and water can contribute, but usually at much lower levels.

Question 28Radon Measurement Fundamentals and Physics

Which unit is used to express the concentration of radon gas in air?

  1. Becquerels per kilogram (Bq/kg)
  2. Working level (WL)
  3. Picocuries per liter (pCi/L) Correct answer.
  4. Millirem per year (mrem/y)

Explanation

Radon gas concentration in air is commonly expressed in picocuries per liter (pCi/L) or becquerels per cubic meter (Bq/m³). WL is used for progeny, and mrem/y is a dose unit.

Question 29Radon Measurement Fundamentals and Physics

A radon measurement device is placed in a home and records an average of 4.0 pCi/L over a 48-hour closed-house test. What does this result primarily represent?

  1. The radon concentration during the test period under closed-house conditions Correct answer.
  2. The radon concentration in the soil beneath the home
  3. The annual average radon concentration for the home
  4. The radon progeny concentration expressed as working levels

Explanation

A short-term test measures radon concentration over the test period under controlled conditions. It does not directly give the annual average or soil gas concentration.

Question 30Radon Measurement Fundamentals and Physics

Which factor would most likely cause a short-term radon test to underestimate the long-term average radon concentration in a home?

  1. Testing during a season when the house is well ventilated Correct answer.
  2. Placing the detector in a room with closed windows and doors
  3. Conducting the test during a period of unusually high winds
  4. Testing in the lowest livable level of the home

Explanation

Good ventilation increases air exchange and dilutes indoor radon, leading to lower measured concentrations. Short-term tests can miss seasonal variations, so testing during a well-ventilated period may underestimate the annual average.

Question 31Radon Measurement Fundamentals and Physics

A homeowner wants to know the average radon concentration over a full year. Which measurement approach is most appropriate?

  1. A long-term alpha track detector deployed for 12 months Correct answer.
  2. A continuous monitor recording for 1 week
  3. A grab sample collected in a syringe
  4. A 2-day charcoal canister test

Explanation

Long-term tests of at least 90 days, and ideally 12 months, better capture seasonal variations and provide a more representative annual average. Short-term tests are useful for screening but are less representative.

Question 32Radon Measurement Fundamentals and Physics

Two adjacent homes have similar soil radium content, but one has a much higher indoor radon concentration. Which explanation best accounts for this difference?

  1. The home with lower radon has a higher indoor temperature, which destroys radon gas.
  2. The home with higher radon has more open windows, allowing radon to accumulate.
  3. The home with lower radon has a deeper basement, which blocks soil gas.
  4. The home with higher radon has a more airtight foundation and greater pressure-driven soil gas entry. Correct answer.

Explanation

Radon entry depends on soil permeability, foundation integrity, and pressure differences. An airtight home can sustain a stack effect that draws soil gas indoors, increasing radon levels even with similar soil radium.

Question 33Radon Measurement Fundamentals and Physics

A continuous radon monitor records a sudden, temporary increase in radon concentration immediately after being placed in a home. Which factor is the most likely cause?

  1. Radon progeny plate-out on the detector's sensor
  2. A malfunction in the detector's calibration
  3. The detector's response to changes in barometric pressure
  4. A pressure-driven influx of soil gas caused by the building's HVAC system Correct answer.

Explanation

HVAC operation can create pressure differences that draw soil gas into the home, causing short-term spikes. Monitors may also show spikes due to other transient events, but HVAC-induced pressure changes are a common cause.

Question 34Radon Measurement Fundamentals and Physics

Why is radon-222 considered the primary health concern among radon isotopes in indoor air?

  1. It is the only isotope that is chemically reactive.
  2. It is the only isotope that can enter buildings through soil.
  3. It is the most abundant isotope and its decay products emit alpha particles. Correct answer.
  4. It has the shortest half-life and decays most rapidly.

Explanation

Radon-222 is the most abundant isotope in indoor air and its short-lived progeny emit alpha particles that can damage lung tissue. Other isotopes are less abundant or have shorter half-lives that limit their accumulation.

Question 35Radon Entry, Transport, and Building Dynamics

Which driving force is primarily responsible for radon entry into a house from the surrounding soil?

  1. Pressure-driven soil gas flow from the building's depressurization Correct answer.
  2. Convective mixing caused by wind over the roof
  3. Diffusion of radon through concrete slabs only
  4. Capillary action drawing soil water upward

Explanation

The dominant entry mechanism is advective soil gas flow driven by the small pressure difference between soil and the building interior, created by stack effect, exhaust fans, and wind. Diffusion contributes but is minor compared to pressure-driven flow.

Question 36Radon Entry, Transport, and Building Dynamics

The stack effect in a heated building in winter generally produces which pressure relationship at the base of the building?

  1. Negative pressure indoors relative to soil Correct answer.
  2. Neutral pressure throughout the building envelope
  3. Oscillating pressure with no net difference
  4. Positive pressure indoors relative to soil

Explanation

Warm indoor air is buoyant and rises, leaving the lower portion of the building under suction relative to the soil. This depressurization at the base draws soil gas inward.

Question 37Radon Entry, Transport, and Building Dynamics

A homeowner runs a large bathroom exhaust fan continuously. How does this most likely affect radon entry?

  1. It reverses the stack effect and pressurizes the base
  2. It reduces entry by diluting indoor air
  3. It has no measurable effect on radon entry
  4. It increases entry by depressurizing the house relative to soil Correct answer.

Explanation

Exhaust fans remove indoor air and lower indoor pressure, increasing the soil-to-indoor pressure difference and thus advective soil gas entry. The effect is strongest when makeup air is limited.

Question 38Radon Entry, Transport, and Building Dynamics

Which soil characteristic most strongly increases the rate of pressure-driven radon entry into a building?

  1. High air permeability with high radium content Correct answer.
  2. Low soil moisture with low porosity
  3. Dense bedrock with no fractures
  4. High clay content with low permeability

Explanation

High permeability allows soil gas to move readily toward the building, and high radium content supplies the radon source. Together they maximize advective entry.

Question 39Radon Entry, Transport, and Building Dynamics

Radon that enters a home from a private well used for showering and other household uses is best described as entering via which pathway?

  1. Emanation from building materials
  2. Soil gas advection through the slab
  3. Water supply degassing into indoor air Correct answer.
  4. Diffusion from outdoor ambient air

Explanation

Radon dissolved in groundwater is released into indoor air when water is agitated, heated, or sprayed, such as during showers. This is the water-supply pathway.

Question 40Radon Entry, Transport, and Building Dynamics

In a house with a basement, where is radon concentration typically highest when soil is the main source?

  1. Outdoor porch
  2. Lowest livable level, such as the basement Correct answer.
  3. Attic space
  4. Upper-floor bedrooms

Explanation

Radon is denser and enters primarily at the base of the building where depressurization and soil contact are greatest. Concentrations therefore tend to be highest at the lowest livable level.

Question 41Radon Entry, Transport, and Building Dynamics

Which building feature most commonly provides a direct soil-gas entry route in a slab-on-grade home?

  1. Insulated exterior walls
  2. Roof vents
  3. Double-pane windows
  4. Cracks and penetrations in the slab Correct answer.

Explanation

Cracks, control joints, and utility penetrations in the slab create openings through which pressure-driven soil gas enters. These are classic entry points.

Question 42Radon Entry, Transport, and Building Dynamics

A sub-slab depressurization system reduces indoor radon primarily by doing what?

  1. Filtering radon out of the soil before it enters
  2. Sealing all cracks in the foundation
  3. Reversing the building's stack effect permanently
  4. Creating a negative pressure field under the slab that draws soil gas away from the building Correct answer.

Explanation

Sub-slab depressurization uses a fan to lower pressure beneath the slab relative to the building, so soil gas is collected and vented outdoors rather than drawn inside. It does not remove radon from soil or seal every opening.

Question 43Radon Entry, Transport, and Building Dynamics

During winter, a two-story house shows higher radon in the basement than in summer. Which explanation best accounts for this seasonal pattern?

  1. Greater indoor-outdoor temperature difference strengthens the stack effect Correct answer.
  2. Outdoor radon concentration rises in winter
  3. Soil radium content increases in winter
  4. Radon decay products become heavier in cold air

Explanation

A larger indoor-outdoor temperature difference in winter increases buoyancy-driven depressurization at the base, enhancing soil gas entry. Soil radium content itself does not change seasonally.

Question 44Radon Entry, Transport, and Building Dynamics

A home has a crawlspace with an open vent to the living space above. How does this configuration affect radon transport?

  1. It eliminates the stack effect in the house
  2. It blocks soil gas from reaching the living space
  3. It allows soil gas accumulating in the crawlspace to move into the living area Correct answer.
  4. It converts radon into decay products before entry

Explanation

Soil gas can accumulate in a crawlspace and, if connected to the living space, migrate upward into occupied areas. Pressure and concentration gradients drive this transfer.

Question 45Radon Entry, Transport, and Building Dynamics

Which condition would most reduce pressure-driven radon entry through a basement floor?

  1. Adding a sealed vapor barrier and closing major slab openings Correct answer.
  2. Lowering the neutral pressure level
  3. Running additional exhaust fans in the basement
  4. Increasing the indoor-outdoor pressure difference

Explanation

Closing entry routes and sealing the slab reduces the pathways for advective flow. Reducing openings limits the volume of soil gas that can be drawn in.

Question 46Radon Entry, Transport, and Building Dynamics

Radon movement through intact, low-permeability concrete is dominated by which process?

  1. Diffusion Correct answer.
  2. Turbulent mixing
  3. Capillary wicking
  4. Advective bulk flow

Explanation

When permeability is low and pressure-driven flow is limited, molecular diffusion becomes the dominant transport mechanism through the material. Advection requires connected, permeable pathways.

Question 47Radon Entry, Transport, and Building Dynamics

A house has a strong radon source in soil but very tight, well-sealed construction. What is the most likely effect on indoor radon compared with a leaky house on the same soil?

  1. Tighter construction eliminates the stack effect
  2. Tighter construction always guarantees lower indoor radon
  3. Tighter construction can increase indoor radon by reducing dilution and natural ventilation Correct answer.
  4. Construction tightness has no relationship to indoor radon

Explanation

Tight construction reduces uncontrolled air exchange, which can allow radon to accumulate even though entry openings are fewer. The net effect depends on the balance of entry and ventilation.

Question 48Radon Entry, Transport, and Building Dynamics

Which factor most directly determines the radon source strength of soil beneath a building?

  1. Number of windows
  2. Indoor relative humidity
  3. Radium concentration and emanating fraction of the soil Correct answer.
  4. Roof pitch

Explanation

Source strength depends on how much radium is present and how much of the resulting radon escapes the soil grain into pore space, known as the emanating fraction. Transport then moves it to the building.

Question 49Radon Entry, Transport, and Building Dynamics

An energy-efficient home with a heat recovery ventilator operates balanced supply and exhaust. How does this generally affect radon compared with unbalanced exhaust-only ventilation?

  1. Balanced ventilation always increases soil gas entry
  2. Balanced ventilation tends to avoid net house depressurization and can reduce entry Correct answer.
  3. Exhaust-only ventilation reduces entry by depressurizing the house
  4. Ventilation type has no effect on radon entry

Explanation

Balanced ventilation supplies and exhausts comparable airflows, minimizing net indoor depressurization that drives soil gas entry. Exhaust-only systems can depressurize the house and increase entry.

Question 50Radon Entry, Transport, and Building Dynamics

Which statement best describes the neutral pressure level in a building?

  1. The point of maximum radon concentration
  2. The depth at which soil radon is highest
  3. The level at which the fan is installed
  4. The elevation where indoor and outdoor pressures are equal Correct answer.

Explanation

The neutral pressure level is the height at which indoor and outdoor pressures balance, with suction below and positive pressure above in a stack-driven building. Its position influences where soil gas is drawn in.