What regular assessment must be conducted if PJM's systems are down?

The correct choice is determined by the established protocol for monitoring the situation when PJM's systems experience downtime. Regular assessments are critical during such occurrences to ensure that any complications are quickly identified and addressed. In this context, conducting assessments every 20 minutes provides a balance between frequency and manageability, allowing for timely updates on system status and any potential operational impacts. This interval enables PJM to maintain an ongoing awareness of the situation, facilitating quicker decision-making and the implementation of corrective actions if necessary.

The other interval options may either be too frequent, placing unnecessary strain on personnel and resources, or too infrequent, risking delays in response to critical issues. Therefore, the 20-minute assessment interval is the most effective strategy for maintaining oversight and operational integrity during system downtimes.