According to the Ethical Guidelines of the Tri-Council and the Canadian

According to the ethical guidelines of the Tri-Council and the Canadian Psychological Association, researchers using human subjects must do all of the following EXCEPT:

A) provide adequate financial reimbursement to compensate for the time and effort of their subjects.
B) warn the subjects in advance if any risk exists for those participating in the study.
C) give subjects the opportunity to withdraw from the study at any time without any penalty.
D) explain enough about the study so that subjects can decide whether they wish to participate.