Which system indicates the operational status of the left generator?

The C option, the L-DC Generator CAS message, is the correct answer because it specifically provides real-time feedback on the operational status of the left generator. In aviation and technical systems, a Crew Alerting System (CAS) message is designed to alert operators of any abnormalities or statuses regarding critical components, such as generators. When the system detects an issue with the left generator, it will trigger the appropriate CAS message, allowing the crew to promptly address the situation.

The other options do not focus on the specific operational status of the generator. For instance, a battery ammeter measures the current flowing in and out of the battery but does not directly indicate the operational status of individual generators. Similarly, a loadmeter displays the electrical load being generated or consumed but does not specifically inform operators about which generator is functioning or if there are issues. Lastly, the exterior lighting control is unrelated to the operational status of the generators, as it pertains to managing external illumination rather than monitoring power generation systems. Thus, only the L-DC Generator CAS message serves the purpose of indicating the operational status of the left generator.