Since the project manager cannot avoid, transfer, or mitigate the risk, the only remaining option is to accept the risk and develop a contingency plan to handle it if it occurs.

According to the PMI-RMP Exam Content Outline1, one of the tools and techniques for risk response planning is risk response strategies. These are the actions that the project manager and the project team take to address the identified risks, either positive or negative. For negative risks or threats, the PMI-RMP Exam Content Outline1 lists four possible strategies: avoid, transfer, mitigate, and accept.

Avoid risk means changing the project plan to eliminate the threat or its impact2. For example, changing the scope, schedule, or budget to avoid a risk.

Transfer risk means shifting the impact of a threat to a third party, such as a contractor, vendor, or insurer2. For example, buying insurance, outsourcing, or using performance bonds to transfer a risk.

Mitigate risk means reducing the probability and/or impact of a threat2. For example, conducting more tests, adopting best practices, or providing training to mitigate a risk.

Accept risk means acknowledging the existence of a threat and being willing to deal with its consequences2. For example, doing nothing, establishing a contingency reserve, or developing a contingency plan to accept a risk.

In this question, the project manager has determined that they cannot outsource work (transfer) nor eliminate the scope (avoid). They also discover that they cannot buy insurance (transfer) or mitigate the risk. Therefore, the only remaining option is to accept the risk. Accepting the risk does not mean ignoring the risk, but rather recognizing it and preparing for its potential occurrence and impact. Therefore, the best answer is D.