Final answer:
Cockpit voice recorders must continuously record from the moment electrical power is first supplied to the recorder, which is option C.
Step-by-step explanation:
The student's question pertains to the operational protocols for aircraft cockpit voice recorders (CVRs). Cockpit voice recorders are designed to continuously record the audio environment in the flight deck for the purpose of incident and accident investigation. According to aviation regulations, CVRs must start recording from the moment electrical power is first supplied to the recorder, which often occurs before engine start. Therefore, the correct response would be that cockpit voice recorders must be continuously recording from the time electrical power is first provided to the recorder, which corresponds to option C.