I believe it's A. Premature Birth (though they all seem pretty believable)
Your blood vessels dilate which is called vasodilation, this allows your blood to carry out the excess heat from inside your body to the outside.
Nucleus to the ribosomes, I think.
The answer is (A) stabilizing selection. Stabilizing selection favors the average in a population. In this case, babies that are born at a normal body weight, or an average between the two extremes of underweight and large, tend to have more favorable outcomes.
Demonstrative pronoun is the answer.