What is statement is true concerning the term "isochronous" as it applies to prime mover speed control governors?

Correct Answer: Option C — Isochronous governors are able to maintain constant prime mover speed regardless of load by employing temporary speed droop.

Isochronous governors maintain a constant engine speed regardless of load by utilizing temporary speed droop. This mechanism allows the governor to respond to load changes without a permanent change in steady-state speed, ensuring precise frequency control in electrical power generation applications where constant speed is critical for system stability.