Which of the following components is part of a vehicle's fuel system?

The fuel injector is a crucial component of a vehicle's fuel system because it is responsible for delivering the correct amount of fuel to the engine's combustion chamber. This process involves spraying a fine mist of fuel into the air stream in order to create an optimal mixture for combustion, which is essential for efficient engine performance and emissions control.

In contrast, the alternator is part of the electrical system, providing power to the vehicle’s electrical components and charging the battery. The starter motor is responsible for starting the engine by cranking it and initiating the combustion process. The thermostat, on the other hand, is a component of the cooling system, regulating the engine's temperature by controlling the flow of coolant. Each of these components plays a vital role in the vehicle's operation, but only the fuel injector is directly involved in the fuel system.