[Reviews of the Circulatory System]
2. What is happening in the heart when the semi-lunar valves are closed?

I. Blood is entering the aorta.

II. Blood is entering the pulmonary artery.

III. Blood is entering the ventricles.

IV. The ventricles are contracting.

A) I and II only

B) I and III only

C) III only

D) III and IV only

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Slichter