The Problem with Relying on Participants Whose Brains Have Been

The problem with relying on participants whose brains have been accidentally damaged in order to understand brain functioning is that

A) researchers have no control over the location or extent of the damage.
B) people with damaged brains no longer allow themselves to be studied by researchers.
C) the brain damage is never extensive enough and does not produce noticeable changes in behavior.
D) governmental agencies prohibit research with people who have suffered damage to their brains.