What Causes the Cardiac Valves to Open and Close

Multiple Choice

What causes the cardiac valves to open and close?

A) Chordae tendineae contract and relax to open and close the valves.
B) Papillary muscles contract and relax to open and close the valves.
C) As the walls of the heart's chambers stretch or relax, they send nervous impulses to the valves, stimulating them to open or close.
D) Pressure changes in the cardiac chambers cause the valves to open and close.