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CPE II practice questions

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Question 1Engineering Fundamentals and Applied Science

A 5 kg block rests on a horizontal surface with a coefficient of static friction of 0.30. What is the minimum horizontal force needed to start the block sliding? (Use g = 9.81 m/s².)

  1. 9.8 N
  2. 49.1 N
  3. 14.7 N Correct answer.
  4. 24.5 N

Explanation

The maximum static friction force equals μs times the normal force, and on a horizontal surface the normal force equals the weight mg = 5 × 9.81 = 49.05 N. Multiplying by 0.30 gives about 14.7 N, which is the threshold force required to initiate motion.

Question 2Engineering Fundamentals and Applied Science

In a steady-state heat conduction problem through a plane wall, which quantity remains constant across the wall thickness?

  1. Heat flux Correct answer.
  2. Temperature
  3. Thermal conductivity
  4. Temperature gradient magnitude

Explanation

At steady state with no internal generation, energy conservation requires that the same heat rate pass through every cross-section, so the heat flux q″ is uniform. The temperature gradient adjusts inversely with conductivity, and temperature itself decreases linearly only when conductivity is constant.

Question 3Engineering Fundamentals and Applied Science

A simply supported beam of span L carries a concentrated point load P at midspan. What is the maximum bending moment?

  1. PL/4 Correct answer.
  2. PL
  3. PL/8
  4. PL/2

Explanation

The reactions at each support are P/2 by symmetry. The bending moment at midspan is the reaction times the half-span, giving (P/2)(L/2) = PL/4, which is the maximum moment for this loading.

Question 4Engineering Fundamentals and Applied Science

A pump delivers 0.02 m³/s of water through a pipe of 0.10 m internal diameter. What is the average flow velocity?

  1. 5.09 m/s
  2. 1.27 m/s
  3. 0.64 m/s
  4. 2.55 m/s Correct answer.

Explanation

Continuity gives velocity as volumetric flow divided by cross-sectional area. The area is π(0.05)² = 0.00785 m², and 0.02 divided by 0.00785 yields approximately 2.55 m/s.

Question 5Engineering Fundamentals and Applied Science

Which dimensionless group characterizes the ratio of inertial forces to viscous forces in a flowing fluid?

  1. Mach number
  2. Froude number
  3. Prandtl number
  4. Reynolds number Correct answer.

Explanation

The Reynolds number, ρVD/μ, compares inertial to viscous effects and determines whether flow is laminar or turbulent. The other groups compare different force balances or transport properties.

Question 6Engineering Fundamentals and Applied Science

A 10 Ω resistor and a 40 Ω resistor are connected in parallel across a 120 V source. What is the total current drawn from the source?

  1. 2.4 A
  2. 12 A
  3. 15 A Correct answer.
  4. 3.0 A

Explanation

Each branch draws current independently: 120/10 = 12 A and 120/40 = 3 A, so the source supplies 15 A total. Equivalently, the parallel equivalent resistance is 8 Ω, and 120/8 = 15 A.

Question 7Engineering Fundamentals and Applied Science

In a three-phase balanced system, the line-to-line voltage is 480 V. What is the phase voltage for a wye-connected load?

  1. 480 V
  2. 831 V
  3. 240 V
  4. 277 V Correct answer.

Explanation

For a wye connection, phase voltage equals line voltage divided by √3. Dividing 480 by 1.732 gives approximately 277 V, the standard phase-to-neutral value in 480 V systems.

Question 8Engineering Fundamentals and Applied Science

Which law states that the induced electromotive force in a circuit is proportional to the negative rate of change of magnetic flux through it?

  1. Ampere's law
  2. Ohm's law
  3. Coulomb's law
  4. Faraday's law Correct answer.

Explanation

Faraday's law expresses induced emf as −dΦ/dt, with the negative sign reflecting Lenz's law on the direction of opposition. It is the basis for transformers and generators.

Question 9Engineering Fundamentals and Applied Science

A control system has an open-loop transfer function with a single pole at the origin. What is the steady-state error to a unit step input for a unity-feedback configuration?

  1. Zero Correct answer.
  2. Infinite
  3. Undefined without the gain
  4. Finite and nonzero

Explanation

A single integrator in the forward path makes the system Type 1, which tracks a step input with zero steady-state error. The velocity-error constant is finite, so errors arise only for ramp inputs.

Question 10Engineering Fundamentals and Applied Science

A steel rod of original length 2.0 m is subjected to a tensile strain of 0.0015. What is its elongation?

  1. 1.5 mm
  2. 0.30 mm
  3. 3.0 mm Correct answer.
  4. 6.0 mm

Explanation

Strain is elongation divided by original length, so elongation equals strain times length: 0.0015 × 2.0 m = 0.003 m, or 3.0 mm.

Question 11Engineering Fundamentals and Applied Science

Which material property describes a metal's resistance to localized plastic deformation such as indentation?

  1. Toughness
  2. Ductility
  3. Stiffness
  4. Hardness Correct answer.

Explanation

Hardness measures resistance to localized surface deformation and is commonly assessed by indentation tests such as Brinell or Rockwell. The other properties describe energy absorption, plastic elongation, or elastic modulus.

Question 12Engineering Fundamentals and Applied Science

A Carnot engine operates between 600 K and 300 K. What is its thermal efficiency?

  1. 67%
  2. 33%
  3. 25%
  4. 50% Correct answer.

Explanation

Carnot efficiency is 1 minus the ratio of cold to hot absolute temperature: 1 − 300/600 = 0.50. This is the maximum possible efficiency for any engine operating between these reservoirs.

Question 13Engineering Fundamentals and Applied Science

In an ideal Rankine cycle, which component raises the pressure of the working fluid from condenser pressure to boiler pressure?

  1. Pump Correct answer.
  2. Condenser
  3. Boiler
  4. Turbine

Explanation

The pump pressurizes the liquid condensate before it enters the boiler, consuming a small fraction of the cycle work. The turbine expands the vapor, while the boiler and condenser exchange heat at nearly constant pressure.

Question 14Engineering Fundamentals and Applied Science

A four-bar linkage has a crank that can rotate fully through 360 degrees. What is this linkage configuration called?

  1. Double-rocker
  2. Grashof crank-rocker Correct answer.
  3. Structure
  4. Change-point linkage

Explanation

When the Grashof condition holds and the shortest link is the input, the linkage becomes a crank-rocker because that link can revolve fully while the output link oscillates. Grashof's inequality requires the sum of shortest and longest links to be no greater than the sum of the other two.

Question 15Engineering Fundamentals and Applied Science

A gear train has a driving gear with 20 teeth meshing with a driven gear of 60 teeth. What is the speed ratio of driver to driven?

  1. 3:1 Correct answer.
  2. 1:2
  3. 1:3
  4. 1:1

Explanation

Speed ratio of driver to driven equals the tooth count of the driven gear divided by that of the driver: 60/20 = 3, so the driver turns three times for each driven revolution. Torque is multiplied by the same factor in the opposite direction.

Question 16Engineering Fundamentals and Applied Science

Which binary number is equivalent to the decimal value 13?

  1. 1001
  2. 1011
  3. 1110
  4. 1101 Correct answer.

Explanation

Decimal 13 decomposes as 8 + 4 + 1, giving binary 1101. Each bit position represents a power of two, and summing the set bits must reproduce the decimal value.

Question 17Engineering Fundamentals and Applied Science

In a logic circuit, a two-input NAND gate is fed inputs A = 1 and B = 0. What is the output?

  1. Undefined
  2. High impedance
  3. 1 Correct answer.
  4. 0

Explanation

A NAND gate outputs the inverse of the AND result. Since 1 AND 0 is 0, the NAND output is 1.

Question 18Engineering Fundamentals and Applied Science

A tensile specimen of initial gage length 50 mm fractures at a final gage length of 60 mm. What is the percent elongation?

  1. 16.7%
  2. 20% Correct answer.
  3. 10%
  4. 25%

Explanation

Percent elongation is the change in length divided by the original length, times 100. The change is 10 mm over 50 mm, giving 0.20 or 20%.

Question 19Engineering Fundamentals and Applied Science

A pipe reduces from a diameter of 0.20 m to 0.10 m. If the velocity in the larger section is 1.5 m/s, what is the velocity in the smaller section for an incompressible fluid?

  1. 6.0 m/s Correct answer.
  2. 3.0 m/s
  3. 0.75 m/s
  4. 0.375 m/s

Explanation

By continuity, velocity scales inversely with the square of diameter. The diameter halves, so the area drops by a factor of four and velocity rises by four: 1.5 × 4 = 6.0 m/s.

Question 20Engineering Fundamentals and Applied Science

What is the primary purpose of a surge tank in a hydroelectric penstock system?

  1. To increase the head available to the turbine
  2. To absorb pressure transients from sudden flow changes Correct answer.
  3. To filter sediment from the water
  4. To cool the generator windings

Explanation

A surge tank provides a free surface near the turbine that absorbs water-hammer pressure surges when flow is suddenly reduced or increased. It protects the penstock from excessive transient pressures.

Question 21Engineering Fundamentals and Applied Science

A simply supported beam with a uniformly distributed load w over span L develops a maximum bending moment of wL²/8. If the span doubles while the load per unit length stays constant, by what factor does the maximum moment change?

  1. 2
  2. 16
  3. 8
  4. 4 Correct answer.

Explanation

The moment scales with L², so doubling the span multiplies the moment by 2² = 4. This quadratic dependence explains why long spans are far more sensitive to distributed loading.

Question 22Engineering Fundamentals and Applied Science

A first-order system has a time constant of 4 s. Approximately how long does the response take to reach 95% of its final value after a step input?

  1. 8 s
  2. 4 s
  3. 12 s Correct answer.
  4. 20 s

Explanation

A first-order step response reaches about 95% after three time constants, since 1 − e⁻³ ≈ 0.95. With τ = 4 s, that is approximately 12 s.

Question 23Engineering Fundamentals and Applied Science

During a tensile test, a metal exhibits a linear elastic region followed by a yield point and then strain hardening. Which point on the stress-strain curve defines the proportional limit?

  1. The stress at fracture
  2. The point where the curve first deviates from linearity Correct answer.
  3. The point where plastic deformation begins permanently
  4. The maximum stress the material can sustain before necking

Explanation

The proportional limit is the stress at which the stress-strain relationship stops being linear, marking the end of direct proportionality. Yielding and plastic deformation begin at or slightly above this point, and ultimate strength and fracture occur later.

Question 24Engineering Fundamentals and Applied Science

A heat engine receives 500 kJ of heat and rejects 350 kJ to a cold reservoir per cycle. What is its thermal efficiency?

  1. 43%
  2. 30% Correct answer.
  3. 35%
  4. 70%

Explanation

Efficiency is net work divided by heat input. The net work is 500 − 350 = 150 kJ, and 150/500 = 0.30, or 30%.

Question 25Engineering Fundamentals and Applied Science

In a DC motor, what happens to the back emf as the rotor speeds up under no load?

  1. It remains constant regardless of speed
  2. It decreases toward zero
  3. It reverses polarity
  4. It increases toward the supply voltage Correct answer.

Explanation

Back emf is proportional to flux and rotational speed, so it grows as the rotor accelerates. At no load it approaches the supply voltage, leaving only enough net voltage to overcome losses.

Question 26Engineering Fundamentals and Applied Science

In a binary vapor power cycle, why is mercury sometimes paired with water as the working fluid in the low-pressure stage?

  1. Mercury's high critical temperature lets it reject heat at a temperature above water's boiling point Correct answer.
  2. Mercury condenses at a very low temperature, improving the vacuum
  3. Mercury has a higher specific volume than steam at the same pressure
  4. Mercury has a low latent heat of vaporization that reduces condenser duty

Explanation

A mercury topping cycle condenses mercury at a temperature high enough to boil water in the bottoming cycle, which reduces irreversibility in the heat addition process and raises overall cycle efficiency. The key property is that mercury's saturation temperature at practical condenser pressures exceeds the water boiling temperature, enabling effective heat transfer between the cycles.

Question 27Engineering Fundamentals and Applied Science

A cantilever beam of length L carries a concentrated load P at its free end. What is the maximum deflection at the free end?

  1. PL³/(3EI) Correct answer.
  2. PL⁴/(8EI)
  3. PL³/(8EI)
  4. PL²/(2EI)

Explanation

For a cantilever with an end load, the deflection curve integrates the bending moment to give maximum tip deflection PL³/(3EI). The cubic dependence on length and linear dependence on load and stiffness are characteristic of this standard case.

Question 28Engineering Fundamentals and Applied Science

A hydraulic turbine develops 2.0 MW while the water surface elevation difference across the plant is 50 m. Assuming a turbine efficiency of 0.90, what is the required volumetric flow rate? (Take g = 9.81 m/s², water density 1000 kg/m³.)

  1. 5.03 m³/s
  2. 4.53 m³/s Correct answer.
  3. 45.3 m³/s
  4. 22.6 m³/s

Explanation

Hydraulic power available is ρgQH, and the shaft power is efficiency times that value. Solving Q = P/(ηρgH) gives 2.0×10⁶/(0.90×1000×9.81×50) ≈ 4.53 m³/s.

Question 29Engineering Fundamentals and Applied Science

A specimen is loaded in a state of plane stress with σx = 100 MPa, σy = 40 MPa, and τxy = 30 MPa. What is the maximum principal stress?

  1. 110 MPa Correct answer.
  2. 90 MPa
  3. 130 MPa
  4. 70 MPa

Explanation

The principal stresses are given by the average normal stress plus or minus the radius of Mohr's circle. The average is 70 MPa and the radius is √(30² + 30²) ≈ 42.4 MPa, giving a maximum principal stress of about 112 MPa, closest to 110 MPa.

Question 30Engineering Fundamentals and Applied Science

In a reciprocating compressor, what is the effect of clearance volume on volumetric efficiency?

  1. It has no effect because clearance gas does not participate in the cycle
  2. It decreases volumetric efficiency because residual high-pressure gas re-expands on the suction stroke Correct answer.
  3. It decreases volumetric efficiency only at low speeds
  4. It increases volumetric efficiency because residual gas helps compression

Explanation

Clearance gas trapped at discharge pressure re-expands during the suction stroke, reducing the fresh charge drawn in and lowering volumetric efficiency. The larger the clearance ratio, the greater the re-expansion volume and the lower the volumetric efficiency.

Question 31Engineering Fundamentals and Applied Science

A DC shunt generator has an armature resistance of 0.5 Ω and delivers 40 A at 220 V. If the shunt field resistance is 110 Ω, what is the generated emf?

  1. 220 V
  2. 240 V
  3. 230 V Correct answer.
  4. 222 V

Explanation

The field current is 220/110 = 2 A, so the armature current is 40 + 2 = 42 A. The generated emf equals terminal voltage plus armature drop: 220 + 42×0.5 = 241 V, which is closest to 240 V among the choices; the intended answer is 241 V.

Question 32Engineering Fundamentals and Applied Science

Which statement correctly describes the function of a PID controller's integral term?

  1. It provides proportional gain scheduling based on setpoint
  2. It eliminates steady-state offset by accumulating past error Correct answer.
  3. It filters high-frequency noise from the measurement
  4. It responds to the rate of change of the error signal

Explanation

The integral term sums the error over time, so any persistent offset drives the controller output until the error reaches zero, eliminating steady-state offset. The derivative term handles rate of change, and proportional action responds to instantaneous error.

Question 33Engineering Fundamentals and Applied Science

A first-order system with time constant 5 s is subjected to a step input. Approximately what fraction of the final value is reached after 10 s?

  1. 99%
  2. 95%
  3. 63%
  4. 86% Correct answer.

Explanation

For a first-order step response, the output reaches 1 − e^(−t/τ) of its final value. With t/τ = 2, this is 1 − e^(−2) ≈ 0.865, or about 86%.

Question 34Engineering Fundamentals and Applied Science

Which of the following best characterizes a material's fatigue limit?

  1. The stress amplitude at which the S-N curve begins
  2. The stress at which the first microcrack forms in a tensile test
  3. The stress below which a material can endure an unlimited number of cycles without failure Correct answer.
  4. The maximum stress a material can sustain before yielding

Explanation

A fatigue limit, exhibited by many ferrous alloys, is the stress amplitude below which the S-N curve becomes horizontal, meaning the material can survive indefinitely. Nonferrous metals often lack a true limit and instead show a fatigue strength at a specified number of cycles.

Question 35Engineering Fundamentals and Applied Science

A heat pump delivers 12 kW of heating to a space while drawing 4 kW of electrical power. What is its coefficient of performance for heating?

  1. 3.0 Correct answer.
  2. 4.0
  3. 0.33
  4. 2.0

Explanation

Heating COP is the delivered heat divided by the work input, so COP = 12/4 = 3.0. The value exceeds unity because the heat pump moves heat from the cold environment in addition to the work input.

Question 36Engineering Fundamentals and Applied Science

In a simply supported beam of span 6 m carrying a point load of 20 kN at midspan, what is the maximum bending moment?

  1. 60 kN·m
  2. 30 kN·m Correct answer.
  3. 15 kN·m
  4. 120 kN·m

Explanation

For a central point load, the maximum moment equals PL/4, giving 20×6/4 = 30 kN·m at midspan. The reactions are 10 kN each, and the moment at the center is 10 kN × 3 m.

Question 37Engineering Fundamentals and Applied Science

Which dimensionless group is used to characterize whether flow is laminar or turbulent in a pipe?

  1. Froude number
  2. Reynolds number Correct answer.
  3. Prandtl number
  4. Mach number

Explanation

The Reynolds number, ρVD/μ, compares inertial to viscous forces and determines whether pipe flow is laminar or turbulent. Values below roughly 2300 indicate laminar flow, and values above about 4000 indicate turbulent flow in circular pipes.

Question 38Engineering Fundamentals and Applied Science

A 4-bit successive-approximation ADC has a full-scale input of 5.0 V. What is the resolution of this converter?

  1. 0.3125 V Correct answer.
  2. 1.25 V
  3. 0.156 V
  4. 0.625 V

Explanation

Resolution equals full-scale voltage divided by 2ⁿ, where n is the bit count. For 4 bits, 5.0/16 = 0.3125 V per least significant bit.

Question 39Engineering Fundamentals and Applied Science

In a hydrostatic bearing, what primarily supports the applied load?

  1. A thin film of pressurized fluid supplied externally Correct answer.
  2. Magnetic levitation of the shaft
  3. Direct metal-to-metal contact at the bearing surface
  4. Elastohydrodynamic film generated solely by shaft rotation

Explanation

A hydrostatic bearing uses an external pump to pressurize fluid into the clearance gap, so the load is supported by the fluid film even at zero shaft speed. This differs from hydrodynamic bearings, which require rotation to generate the film.

Question 40Engineering Fundamentals and Applied Science

A steel shaft transmits 15 kW at 1500 rpm. What is the torque on the shaft?

  1. 95.5 N·m Correct answer.
  2. 9.55 N·m
  3. 159 N·m
  4. 10 N·m

Explanation

Power equals torque times angular velocity, so T = P/ω with ω = 2π(1500/60) = 157 rad/s. This gives T = 15000/157 ≈ 95.5 N·m.

Question 41Design, Analysis, and Technical Problem Solving

In a peer-to-peer protocol design, two peers must agree on a session key before exchanging application data. Which design choice best limits the exposure of the key if a single long-term credential is later compromised?

  1. Transmit the session key in plaintext inside the first handshake message
  2. Derive a fresh ephemeral session key per connection using a Diffie-Hellman exchange authenticated by the long-term credential Correct answer.
  3. Reuse one static session key across all peers to simplify key distribution
  4. Encrypt all traffic with the long-term credential directly so no negotiation is needed

Explanation

Perfect forward secrecy comes from deriving ephemeral per-connection keys, so compromise of the long-term credential does not reveal past session keys. Authenticating the exchange with the long-term credential still binds the peers' identities. Static or plaintext key distribution defeats this property.

Question 42Design, Analysis, and Technical Problem Solving

A requirements specification states that a transaction log service must never lose a committed record even after a host crash. Which non-functional requirement category does this constraint primarily belong to?

  1. Portability
  2. Usability
  3. Reliability Correct answer.
  4. Localizability

Explanation

Durability of committed data across crashes is a reliability concern, specifically about failure behavior and data integrity. Usability, portability, and localizability address user interaction, platform movement, and language adaptation respectively, not crash-safe persistence.

Question 43Design, Analysis, and Technical Problem Solving

A developer writes a recursive function to compute Fibonacci numbers and finds it slows dramatically for input 40. Analysis shows the same subproblems are recomputed many times. Which technique most directly reduces the asymptotic time complexity?

  1. Increasing the recursion depth limit
  2. Converting recursion to iteration with the same recurrence
  3. Adding logging to each recursive call
  4. Memoizing previously computed subproblem results Correct answer.

Explanation

Memoization caches each subproblem result so it is computed once, reducing exponential recomputation to linear work in the number of distinct subproblems. Plain iteration with the same recurrence still repeats overlapping work unless results are stored. Raising limits or adding logging does not change the algorithm's complexity.

Question 44Design, Analysis, and Technical Problem Solving

In a normalized relational schema, a table stores (OrderID, ProductID, Quantity, ProductName) with primary key (OrderID, ProductID). ProductName depends only on ProductID. Which normalization problem does this represent?

  1. A multivalued dependency violating fourth normal form
  2. A partial dependency violating second normal form Correct answer.
  3. A join dependency violating fifth normal form
  4. A transitive dependency violating third normal form

Explanation

Second normal form requires every non-key attribute to depend on the whole primary key. ProductName depends on only part of the composite key, ProductID, which is a partial dependency. Transitive, multivalued, and join dependencies describe different anomalies addressed by later normal forms.

Question 45Design, Analysis, and Technical Problem Solving

A team must choose between a monolithic deployment and a microservices architecture for a system with a small team and rapidly changing requirements. Which consideration most strongly favors the monolith in this context?

  1. Independent scaling of each functional module
  2. Isolation of failures to a single service boundary
  3. Independent technology stacks per team
  4. Lower operational overhead and simpler cross-module refactoring during early requirement churn Correct answer.

Explanation

With a small team and volatile requirements, a monolith reduces deployment and operational complexity and allows easier refactoring across modules. Independent scaling, failure isolation, and per-team technology choice are benefits of microservices that matter more at larger scale.

Question 46Design, Analysis, and Technical Problem Solving

A function receives an integer parameter representing a day of the month. Which input class should be used first to test boundary behavior?

  1. Only non-numeric strings
  2. Values at the edges of the valid range, such as 1 and 31 Correct answer.
  3. Only typical mid-range values such as 15
  4. Only negative values

Explanation

Boundary value analysis targets the edges of valid and invalid input ranges, where defects cluster. Mid-range values, negative values, and non-numeric strings may be tested too, but the edges of the valid range are the first boundary cases.

Question 47Design, Analysis, and Technical Problem Solving

A web service returns HTTP 401 for a request that carries an expired access token. Which design principle does this response best illustrate?

  1. Idempotency of state-changing operations
  2. Backward-compatible versioning of payloads
  3. Explicit communication of failure cause through standard status semantics Correct answer.
  4. Client-side caching of responses

Explanation

Returning 401 for an invalid or expired credential uses a standard status code to communicate the specific failure cause, enabling clients to react correctly. Idempotency, versioning, and caching are separate concerns not demonstrated by the status choice alone.

Question 48Design, Analysis, and Technical Problem Solving

During analysis of a proposed design, an engineer notes that a queue between two components absorbs bursts but introduces end-to-end latency and duplicate delivery risk. Which statement best characterizes this as a design trade-off?

  1. It trades latency and duplicate handling complexity for improved load smoothing and decoupling Correct answer.
  2. It guarantees exactly-once delivery without additional work
  3. It eliminates the need for error handling between the components
  4. It removes the need to define a retry policy

Explanation

Introducing a queue changes the system's quality attributes: it smooths load and decouples components at the cost of added latency and the need to handle duplicate deliveries. It does not remove error handling or guarantee exactly-once delivery by itself, and retry policy still must be designed.

Question 49Design, Analysis, and Technical Problem Solving

A binary search tree is built by inserting keys in ascending sorted order. What is the resulting height and search complexity in the worst case?

  1. Height log n with O(log n) search
  2. Height n with O(log n) search
  3. Height n with O(n) search Correct answer.
  4. Height log n with O(n) search

Explanation

Inserting sorted keys into an unbalanced binary search tree produces a degenerate chain, so height is n and search degrades to O(n). Balanced height and logarithmic search require a self-balancing tree.

Question 50Design, Analysis, and Technical Problem Solving

A service must process each message from a queue exactly once in effect, even though the broker may redeliver messages after a consumer crash. Which design achieves this?

  1. Acknowledge messages before processing them
  2. Rely on the broker to deduplicate messages automatically
  3. Increase the consumer's prefetch count to reduce redelivery
  4. Make the consumer idempotent by recording processed message identifiers in durable storage Correct answer.

Explanation

Effective exactly-once processing under at-least-once delivery requires idempotent consumers, typically by persisting processed message identifiers and skipping duplicates. Prefetch tuning, early acknowledgment, and assuming broker deduplication do not prevent duplicate side effects.