Research Supports the Idea That Gender Identity Disorders Are Caused

Research supports the idea that gender identity disorders are caused by

A) lack of a same-sex parent model and overprotection by the opposite-sex parent.
B) the child's failure to separate from the parent of the opposite sex.
C) hormonal disturbances or exposure to chemicals during fetal development.
D) a gender identification gene found in twin studies of the disorder.
E) there is actually little support for any theory of the origin of gender identity disorder.