Final answer:
The question suggests the necessity of a safety protocol before starting an engine, which could involve making sure the vehicle is in park or neutral and applies to general safety measures.
Step-by-step explanation:
Always apply at least one safety measure when starting the engine.
When starting an engine, it is important to apply safety measures such as ensuring the vehicle is in "park" or "neutral" (for manual transmission), having the handbrake on, and checking that the area around the vehicle is clear. For a more specific answer, understanding the context of the question is necessary, as it may refer to safety measures, procedural steps, or even mechanical components that should be engaged prior to starting an engine, such as pressing the brake pedal or clutch pedal.