The option "a. Participants are identified by their responses" is not an example of how to treat study participants ethically.
Identifying participants by their responses can potentially compromise their confidentiality and anonymity, which are essential aspects of ethical research practices. Researchers should take measures to protect the privacy and confidentiality of study participants. This includes using anonymized identifiers or coding systems to ensure that individual participants cannot be identified based on their responses.
Respecting participants' privacy and confidentiality is a fundamental ethical principle in research, and researchers should take steps to minimize the risk of harm or unintended consequences that may arise from the identification of participants.