Reviewers have a responsibility to promote ethical peer review by:

The answer

Reviewers promote ethical peer review by providing timely, thorough, objective, and constructive reviews while maintaining confidentiality, disclosing conflicts of interest, and refusing to exploit privileged information. These duties come as a package - each protects the integrity of the process and the rights of the authors whose unpublished work has been entrusted to the reviewer.

Breaking it down: a review should be timely (returned within the agreed window so authors are not left waiting), thorough and constructive (substantive comments that help improve the work, not vague or dismissive remarks), and unbiased (judged on scientific merit, not on the author's identity, institution, nationality, or the reviewer's personal disagreements). The reviewer must maintain confidentiality, treating the manuscript as a privileged document that is not shared, shown to others, or discussed without editor permission. The reviewer must disclose conflicts of interest - financial, personal, or professional - and recuse when a conflict would compromise impartiality. And the reviewer must not use privileged information from the manuscript to advance their own research, delay a competitor, or gain any personal advantage.

Why the other options are wrong

Typical distractors on this CITI item describe unethical conduct dressed up as diligence. "By sharing the manuscript with colleagues or students without permission" violates confidentiality, even if the intent is to get extra opinions - the editor must authorize any additional input. "By using data or ideas from the manuscript in the reviewer's own work" is misappropriation of privileged information and is clearly prohibited. "By deliberately delaying a review to slow down a competing lab" is a serious breach that harms authors and corrupts the process. "By recommending rejection to eliminate competition" substitutes self-interest for objective judgment.

Each of these fails because it puts the reviewer's interests, convenience, or biases ahead of a fair, confidential, and impartial evaluation - the exact opposite of what ethical peer review requires.

The bigger picture

Peer review works only because authors trust that an anonymous expert will judge their work fairly and keep it secret until publication. The reviewer holds real power: access to unpublished ideas and the ability to influence whether the work is published. Ethical obligations exist to prevent abuse of that power. If a reviewer discovers they lack the expertise to judge part of the work, the ethical move is to tell the editor rather than bluff. If they recognize the authors and have a competing interest, they should decline. If they suspect plagiarism or misconduct in the manuscript, they should confidentially alert the editor rather than acting unilaterally. In short, ethical peer review is defined by fairness, confidentiality, transparency about conflicts, and respect for the authors' intellectual property - and reviewers promote it by embodying all of those at once.