A heart murmur is due to

Correct Answer: A

Rationale: A heart murmur is typically caused by leaky or improperly functioning valves.

Correct Answer: C

Rationale: Venous return depends on factors like skeletal muscle contraction, respiration, and total blood volume but is independent of the speed of blood flow itself.

Correct Answer: C

Rationale: The renal veins drain blood from the kidneys.

Correct Answer: C

Rationale: The pulmonary semilunar valve is located at the base of the pulmonary trunk and prevents backflow of blood into the right ventricle after contraction.

Correct Answer: D

Rationale: The left ventricle has the thickest myocardium because it must generate sufficient force to pump blood throughout the entire body via the systemic circulation.