Which of the following is NOT part of a car's drivetrain?

The drivetrain of a car is responsible for transmitting power from the engine to the wheels, and it typically includes components such as the axle, differential, and transmission. However, the component identified as a rotor does not fit into the standard categories associated with a vehicle's drivetrain.

To clarify, a rotor is generally associated with braking systems. In disc brakes, the rotor is the circular metal component that the brake pads grip to slow down the vehicle. While critical to vehicle operation, rotors play a role in the vehicle's braking system, not its drivetrain.

In contrast, the axle connects the wheels to the drivetrain, allowing for power transfer and supporting the vehicle’s weight. The differential enables the wheels to rotate at different speeds, particularly useful when turning. The transmission controls the vehicle's power output by managing gear ratios, allowing the vehicle to accelerate smoothly.

Thus, identifying the rotor as not being part of the drivetrain is accurate, as it serves a function outside of transmitting engine power to the vehicle's wheels.