Normal heart sounds are caused by which of the following events?
a. excitation of the sa node
b. closure of the heart valves
c. friction of blood against the chamber walls
d. opening and closing of the heart valves

Normal sounds of heart are caused due to "opening and closing of heart valves".

Option D

Explanation:

The two noteworthy sounds heard in the ordinary heart sound like "lub and dub". The “lub" is the main heart sound, generally named S1, and is brought about by the closing of mitral and tricuspid valves toward the beginning of systole.  

The subsequent sound,"dub" or S2, is brought about by the closing of aortic and pulmonic valves, denoting the end of the systole

answer: tell your parents first, and wait another couple of days. if it gets any worse, then you should call and ask. and you can always take pain meds if need be.

explanation: