Biological Factors Play a Role in Mental Disorders

Biological factors play a role in mental disorders.Which of the following is NOT a piece of evidence provided in your textbook to support this idea?

A) Medications developed for conditions other than mental disorders have provided clues linking neurotransmitters to certain mental disorders.
B) Fraternal twins are eight times more likely to have the same mental disorders as are unrelated strangers.
C) Exposure to environmental toxins in childhood and adolescence is associated with mental disorders.
D) PET scans demonstrate that some brain regions function differently in people with mental disorders.