Which of the Following Is the Safest Statement to Make

Which of the following is the safest statement to make regarding the origin of gender differences?

A) Hormonal differences between the sexes account for the largest proportion of the variation.
B) The fact that males tend to exhibit more cerebral specialization than females explains the bulk of the differences.
C) The reinforcement children receive for displaying gender-appropriate behavior determines the differences.
D) As with anything, the explanation of gender differences is complex and must take into account both biological and environmental factors.