Final answer:
The correct answer is B. Right and left ventricles. These are the chambers that have just emptied when the second heart sound, S2, is heard as the semilunar valves close.
Step-by-step explanation:
The heart sound that is referred to when discussing the chambers of the heart that have just emptied is known as the second heart sound or S2, commonly characterized as the "dub" sound. This sound is produced when the semilunar valves close at the end of ventricular systole and the beginning of ventricular diastole. When the S2 sound is heard, the ventricles have just finished contracting and ejecting blood into the pulmonary artery and aorta, and thus, they are the chambers that have just emptied. This places us at the phase known as atrial diastole, ventricular systole, indicating that the correct answer is B. Right and left ventricles.
Your final answer in two line explanation: The second heart sound, S2, occurs when the semilunar valves close, indicating that the ventricles have just emptied their blood into the respective arteries. Hence, the chambers that have just emptied at the hearing of S2 are the right and left ventricles.