Answer: D. Protect identifiable research information from compelled disclosure.
A Certificate of Confidentiality is a document issued to protect sensitive information from being divulged. It is used to protect information from being leaked out by subjects of an investigation. It is a legal document that prevents subjects from being compelled to disclose information regarding a research study. This prevents identifiable research from being leaked by candidates through compulsive speech. Although they provide protection from compulsive speech, any researcher can willingly divulge research information with the consent of the candidates. Apart from compelled disclosure, Certificates of Confidentiality cannot be used to ensure the airtight nature of research information, so other measures need to be taken.