Adopted Children Are Somewhat Overrepresented in Psychiatric Populations

Adopted children are somewhat overrepresented in psychiatric populations. Which of the following is the most suitable explanation?

A) Adopted children are less adequately parented.
B) Adopted childrens peers often say things that make them feel insecure about the normality of their situation.
C) Parents generally do not inform children of their adoption until they are adults.
D) Adopted children on average come from biological backgrounds involving a lot of emotional problems.
E) Finding birth parents is a traumatic and emotionally devastating event.