The best answer would be C, reassess risks with a new assumptions and constraints analysis. When a risk event occurs that was not previously identified, it is important for the project manager to review the project's risk management plan and identify any potential gaps or weaknesses in the risk identification process. One way to do this is to perform a new assumptions and constraints analysis to identify any potential risks that may have been overlooked or underestimated. This can involve reviewing the project's assumptions, constraints, and dependencies, as well as examining any changes that may have occurred since the initial risk assessment was conducted. By performing a new assumptions and constraints analysis, the project manager can identify any new or emerging risks that may impact the project, and can develop appropriate response strategies to mitigate or reduce the impact of those risks. This can help to ensure that the project is able to effectively manage risks throughout the project lifecycle and avoid similar risks in the future.