According to the PMBOK Guide, the project manager is responsible for managing the project team and ensuring that the team members perform their roles and responsibilities in an ethical manner1. The project manager should also apply the PMI Code of Ethics and Professional Conduct2, which states that project managers should respect the confidentiality and privacy of others3. If a team member violates the ethical standards, the project manager should address the issue promptly and constructively4. The best way to do this is to speak with the key team member to clarify the situation, understand the reasons behind the breach, and explain the consequences and expectations. This will help to resolve the conflict, restore trust, and prevent further escalation.

The other options are not the best ways to handle the situation, because they do not involve direct communication or problem-solving with the key team member. Option A is too passive and may imply that the project manager is not capable of managing the team. Option C is too collective and may create more tension or resentment among the team members. Option D is too harsh and may violate the due process or the employment contract of the team member. References:

1: PMBOK Guide, 6th Edition, page 335

2: PMBOK Guide, 6th Edition, page 29

3: PMI Code of Ethics and Professional Conduct, page 5

4: PMBOK Guide, 6th Edition, page 343