Which of the following is a safety issue to check before opening the engine access door?

Answer: C — Engine is shut down

Checking that the engine is shut down is a critical safety measure before opening the engine access door. An operating engine can present numerous hazards, including moving parts, high temperatures, and the risk of electrical shock or fire. By ensuring that the engine is off, you significantly reduce these risks and create a safer environment for performing maintenance or inspections. Other options may relate to safety, but they do not prioritize the immediate risks associated with an operational engine. For instance, while checking for fuel leaks or ensuring the door lock is functioning are important tasks, they do not address the direct danger that comes from an engine that is still running. Therefore, confirming that the engine is shut down is the most fundamental and immediate safety check to make.