Answer:
The first heart sound correspond to the closure of atrioventricular valves which comprises of mitral and transcupid valves.
Explanation:
The first heart sounds is describe as lub and its correspond to the closure of atrioventricular valves which comprises of mitral and triscupid valves because it's coincides with ventricular contractions as the ventricular pressures surpasses the pressure of the atrial which mark the begining of ventricular systole and the end of mechanical diastole. It is a single sound because the mitral and triscupid valves closes simultaneously.
