Which of the following is true about the ignition system of a vehicle?

The ignition system of a vehicle plays a crucial role in starting the engine. It creates the spark necessary to ignite the air-fuel mixture within the engine's cylinders, which is essential for initiating the combustion process that powers the engine. Without a functional ignition system, the engine cannot start because there would be no spark to ignite the fuel. This is why it is correct to say that it is necessary to start the engine.

The other choices, while related to vehicle operation, do not accurately describe the function of the ignition system. For instance, fuel injection is managed by a different system called the fuel injection system, which is responsible for delivering the right amount of fuel to the engine. The cooling system is managed independently to regulate the engine temperature and prevent overheating, while the radio system is powered by the electrical system of the vehicle, not the ignition system. These distinctions highlight the specific and vital role that the ignition system plays in vehicle operation.