A nurse is assisting with teaching a newly licensed nurse about heart sounds. Which of the following sounds is heard when the aortic and pulmonic valves close?

A. Atrial gallop: An atrial gallop is the S4 sound, produced by atrial contraction against a stiff ventricle, not by semilunar valve closure. B. S1: S1 is produced by the closure of the atrioventricular (mitral and tricuspid) valves at the start of systole, not by aortic/pulmonic valve closure. C. Ventricular gallop: A ventricular gallop refers to S3, which follows S2 and indicates rapid ventricular filling, not the sound of semilunar valve closure. D. S2: S2 is produced when the aortic and pulmonic (semilunar) valves close at the end of systole.