In order to start the engine of a commercial motor vehicle, which of the following actions must be taken?

Answer: C — Disengage the clutch

To successfully start the engine of a commercial motor vehicle, it is essential to disengage the clutch. Doing so ensures that the engine can turn over without engaging the transmission, which could potentially lead to a sudden movement of the vehicle and poses a safety risk. Disengaging the clutch allows the vehicle to be in a neutral state, preventing unexpected acceleration or movement that could occur if the vehicle were in gear. While other actions, such as applying the brake pedal, may be necessary for engine start-up safety protocols, they are generally not the primary requirement for starting the vehicle's engine. Overall, disengaging the clutch is crucial for safe engine start-up procedures in commercial vehicles.