Explanation
According to the PMBOK Guide, the risk management process that should be performed in this situation is Plan Risk Responses1. This process involves developing options and actions to enhance opportunities and reduce threats to the project objectives1. In this case, the defect identified during user acceptance testing is a threat that could affect the system performance and the delivery date. Therefore, the project manager should plan risk responses to avoid, mitigate, transfer, or accept the risk, and to implement contingency plans if the risk occurs1. The other options are not appropriate for this situation, as they do not address the need to take action to deal with the risk.
Perform Qualitative Risk Analysis is the process of prioritizing risks based on their probability and impact1. It does not provide options and actions to handle the risks.
Monitor Risks is the process of tracking the implementation of risk responses, identifying and analyzing new risks, and evaluating risk process effectiveness1. It does not involve developing new risk responses.
Perform Quantitative Risk Analysis is the process of analyzing the effect of risks on the project objectives using numerical techniques1. It does not provide options and actions to handle the risks.
References: 1: PMBOK Guide, 7th edition, pages 97-99.