Knowledgeable and Unbiased Observers Have Generally Noted, and Studies Have

Multiple Choice

Knowledgeable and unbiased observers have generally noted, and studies have reliably shown, that psychotherapy is better than no treatment at all for a person who is seriously depressed. My study failed to find a difference. From this I can conclude that

A) psychotherapy really is not effective.
B) my study must have been poorly done.
C) my study may have lacked sufficient power to find a difference.
D) other psychologists don't know what they are talking about.