Why Did Previous Meta-Analysis Data Show That Men Tend to Display

Why did previous meta-analysis data show that men tend to display more helping behavior than women?

A) Psychologists were looking at helping behaviors that are typical of men, overlooking the types of helping behaviors that are typical of women.
B) Psychologists were studying areas that had a disproportionate number of men than women available to help.
C) Psychologists were studying relational helping behaviors, which are more typical of men.
D) The majority of the psychologists at the time were men, which led to bias in the results of gender differences in helping behaviors.