The Nurse Identifies the "LUBB" Sound of the "LUBB/DUBB" of the Cardiac

The nurse identifies the "LUBB" sound of the "LUBB/DUBB" of the cardiac cycle as the sound of the:

A) AV valves closing.
B) closure of the semilunar valves.
C) contraction of the papillary muscles.
D) contraction of the ventricles.