Closure of the atriventricular valve occurs when:
a. the papillary muscle contracts
b. the atrium contracts
c. the valve contracts
d. pressure inside the ventricle is less than pressure inside the atrium
e. pressure inside the ventricle is greater than pressure inside the atrium

The correct answer will be option A.

Explanation:

The atrioventricular valve is one of the four valves present in the heart the function of which is to stop the back flow of the blood from the ventricles to the atrium.  

These valve opens and closes in response to the change in the pressure of the blood in atrium and ventricles.  The valve opens when blood is pumped form the atrium to ventricles which causes the papillary muscles to relax while the valve closes when the ventricles push the blood to the arteries. This causes the papillary muscle to contract which causes the chordate tendineae to create tension ad close the valve.

Thus, option A is the correct answer.

the answers are a and c

the correct answer is - d. china has a large and growing population.

the fact that china has a large (the biggest) population, and it is still growing, doesn't hinder the agriculture production in the country. in fact, it can for increased production in the agriculture, since there's more labor force, as well the sheer mass of people produces lots of scientists that come up with new inventions as to how to improve this sector. nice example is the inner mongolia region in china, in general dominated by the gobi desert, but few scientist came up with a nice idea as to how to make the region productive by using plants that are very resistant to droughts, so lots of people have been employed, and the region is becoming greener and greener each year, and the production of food in this region is also increasing.