Answer:
b.
Explanation:
Heart valves function to ensure a one-way flow of
blood through the heart. The valves are not made
of muscle, but rather are composed of sheets of
tough connective tissue that act like flaps. The
heart valves open and close passively because of
pressure differences on either side of the valve.
When pressure is greater behind the valve, the leaflets are blown open and the blood flows through
the valve. However, when pressure is greater in front of the valve, the leaflets snap shut and blood
flow is stopped.
