What must be done before starting the engine and inspecting inside the cab?

Prior to starting the engine and inspecting the inside of the cab, it is crucial to ensure that the parking brake is engaged and that the gearshift is positioned in neutral. This step is vital for safety, as it prevents the vehicle from moving unexpectedly when the engine is started. If the gearshift is not in neutral or if the parking brake is not set, even a slight mistake could lead to a serious accident, as the vehicle may roll or lurch forward or backward once the engine is running.

Other options, while they might seem relevant, do not address the crucial safety measures needed before starting the vehicle. For example, turning off the radio does not contribute to operational safety, leaving the door open is not a standard safety procedure and could lead to unintentional hazards, and checking the fuel gauge, while important, is not a prerequisite for safely inspecting the cab and starting the engine. Prioritizing the engagement of the parking brake and ensuring the vehicle is not in gear are fundamental steps to protecting the driver and ensuring safe operation of the vehicle.