Answer: a. at the conclusion of data collection
Explanation:
According to Section 8.07 of Ethical Principles of Psychologists and Code of Conduct of the American Psychological Association, Psychologists are not to use deception in research unless the study unless it is not possible to use non-deceptive alternative procedures.
When deception is used, the APA recommends that the participant is told as early as possible of the deception with that being as soon as the participant is no longer participating and failing that, no later than at the conclusion of data collection. Participants are also allowed to decline the use of their data after they discover the deception.