Answer to Question 1
ANS: C
The second heart sound (S2) occurs with the closure of the semilunar (aortic and pulmonic) valves and signals the end of systole. Although it is heard over all the precordium, the S2 is loudest at the base of the heart.
Answer to Question 2
ANS: D
Toward the end of diastole, the atria contract and push the last amount of blood (approximately 25 of stroke volume) into the ventricles. This active filling phase is called presystole, or atrial systole, or sometimes the atrial kick.