More Than a Dozen Studies Have Found That the Probability

More than a dozen studies have found that the probability of a man's becoming gay rises significantly according to the number of older brothers he has.The reason for this "brother effect" appears to be

A) that parents with many male children secretly wish for a daughter and encourage feminine behavior.
B) that a child with older brothers behaves differently to get attention.
C) that the developing brain responds to having so many males in one house.
D) changes in the conditions within the womb caused by previous male pregnancies.