According to the PMBOK Guide, the project manager is responsible for managing the project team and resolving any issues that affect the team performance. The project manager should use interpersonal and team skills, such as conflict management, negotiation, and active listening, to address any issues that arise among the team members. The project manager should also apply problem-solving techniques, such as root cause analysis, to identify and eliminate the underlying causes of the issues. Gathering information and finding the root cause of the problem is the first action that the project manager should take when a junior team member escalates an issue about another member’s interpersonal skills causing the team to be less effective. This will help the project manager to understand the nature and extent of the issue, and to determine the best course of action to resolve it. Having the team members resolve the issue on their own (A) may not be feasible or desirable, as it may lead to further escalation, resentment, or avoidance. Highlighting the impact of their behavior and motivating the team member to make improvements (B) may be a possible action, but not the first one, as it may be premature or ineffective without gathering information and finding the root cause of the problem first. Documenting the escalated issue and addressing it at the end of the project (D) may not be appropriate or responsible, as it may delay or ignore the issue, and negatively affect the team performance and morale. References: PMBOK Guide, 6th edition, pages 349-350, 361-362.