Of the Following,which Is a Valid Criticism of Efficacy Studies

Of the following,which is a valid criticism of efficacy studies of psychotherapy treatments?

A) They show artificially inflated results for mental illnesses of higher severity.
B) They focus on disorder-specific treatments and processes rather than looking at common themes across different disorders.
C) They are only useful in a correlational design; that is,they cannot show cause-and-effect relationships.
D) They take many years to conduct and require very large numbers of participants.