Why Are Modern Researchers Less Convinced That Gender-Related Differences in Cognition

Why are modern researchers less convinced that gender-related differences in cognition and behavior have a physiological basis?

A) Males and females no longer differ much in mathematical abilities, although boys are still overrepresented at the lower and higher extremes.
B) These differences have increased over time due to changes in gender roles.
C) Murder rates are the same in different countries, showing that males are generally more aggressive than females.
D) Males and females now have the same levels of aggression.