Which of the following is NOT a component of a pre-trip inspection?

A pre-trip inspection is a crucial part of ensuring the safety and functionality of a commercial vehicle before operation. It involves checking various components to make sure that everything is in good working condition. Among the essential checks are the engine oil, which ensures the engine is properly lubricated and functioning; wiper blades, which are critical for visibility in inclement weather; and tire condition, which is vital for vehicle stability and safety on the road.

The operation of the radio, while it may contribute to the comfort of the driver, is not considered a necessary safety aspect of a vehicle's pre-trip inspection. The focus is on components that impact the vehicle's operation and safety directly, such as mechanical and functional elements, rather than entertainment devices. Therefore, checking radio operation does not fall under the necessary components of a pre-trip inspection, making it the correct choice in this context.