Gmat Lsat CR里的一道题目

In an experiment, two different types of recorded music were played for neonates in adjacent nurseries in a hospital. In nursery A, classical music was played; in nursery B, rock music was played. After two weeks, it was found that the babies in nursery A cried less, suffered fewer minor ailments, and gained more weight than did the babies in nursery B.

4.        In evaluating the validity of the conclusion suggested by the experiment above, it would be most important to know which of the following?

(A) The musical preferences of the parents of the two groups of newborns

(B) Whether the newborns in both nurseries were equally healthy and happy at the start of the experiment

(C) Whether loud rock music can damage the hearing of newborns

(D) What the average weight of the neonates was before and after the experiment（B）

(E) Whether the music was played in the nurseries at all times or only at certain times