Regarding Mothers and Fathers in Clinical Child Research

Regarding mothers and fathers in clinical child research:

A) Mother and fathers are approximately equally represented in clinical child research
B) Because mothers are more responsible for the development of psychopathology, there is a legitimate reason that mothers are included in research more often than fathers
C) Surprisingly, more fathers are included in clinical child research than mothers
D) More mothers than fathers are included in clinical child research and this pattern is considered problematic by many researchers