Which of the Following Statements About Brain Differentiation Is True

Which of the following statements about brain differentiation is true according to recent findings?

A) The sexual dimorphism of the mammalian brain depends entirely on the presence or absence of testosterone; genes play no direct role.
B) The program of mammalian female brain development unfolds normally in the absence of estradiol or other hormones.
C) There is a single mechanism that accounts for all differences between the brains of male and female mammals.
D) all of the above
E) none of the above