At the instant following the second heart sound, which heart valves are open?

A. Both atrioventricular valves and semilunar valves
B. Atrioventricular valves only
C. All valves are closed
D. Semilunar valves only


Answer: C. All valves are closed

Anatomy & Physiology

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Impaired motor coordination in Parkinson disease is often due to ________.

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Why is there variation in skin color among modern humans?

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