In the context of ethics guidelines in psychological research, deception is ethically allowed

A) only if the study has high internal validity.
B) only in the case of double-blind studies, with or without debriefing.
C) if it is possible to link a participant's identity to his or her data.
D) if the deception is harmless to the participants.

Deception is ethically allowed in psychological research if it is harmless to the participants. The American Psychological Association's Ethical Principles of Psychologists and Code of Conduct state that informed consent should be obtained from participants, except in cases where the research involves minimal risk and the research cannot practically be conducted without deception. However, the deception should not harm participants physically or emotionally. Debriefing should also be conducted to explain the true nature of the study and address any potential harm caused by the deception. Internal validity and participant anonymity are not directly related to the ethical allowance of deception in psychological research.