The correct answer is C.
Insanity defense is also known as mental disorder defense. It is applied in a court of law when the defendant is not responsible for his or her actions due to a persistent psychiatric disease at the time of the criminal act.
The defendant usually admits the action but asserts the lack of culpability based on a mental illness. The defendant is deemed legally incompetent and he/she can not stand trial.
Those found to have been not guilty due to insanity are required to undergo psychiatric treatment in a mental institution.