The atrioventricular valves permit blood flow
a) in both directions.
b) in one direction only.
c) in many directions.
d) from a ventricle to an atrium.
e) in opposite directions on the right and left.

The correct option is B (in one direction)

The two atrioventricular (AV) valves, the mitral valve (bicuspid valve), and the tricuspid valve, which are between the upper chambers (atria) and the lower chambers (ventricles). The two semilunar (SL) valves, the aortic valve and the aspiratory valve, which are in the conduits leaving the heart.  

So the atrioventricular valves enables blood to spill out of the atria to the ventricles. be that as it may, regularly keeps the reverse of blood and opening. ... these valves to open and after that blood goes through from the atria into the ventricles. and afterward when the weight is developing in the ventricles.

1. (1.2kw)x(15/60hours) = .3kwh --> a

2. (5kw)x(90/60hours)x(8cents/kwh) = $0.60 --> d

3. microwave --> 1200 watts = (1.2kw)x(6/60hours) = .12kwh

coffee-maker --> 900 watts = (.9kw)x(10/60hours) = .15kwh

therefore, it requires more energy for the coffee-maker to do the same amount of work.

so the answer is a.

they deliver oxygen to the blood