Explanation:

- The base frame of a car or other wheeled vehicle is called a *chassis*. It serves as the structural foundation, supporting various components like the engine, transmission, and body.

- Option 1, fuselage: This refers to the main body of an aircraft. It contains the cockpit, passenger cabin, and cargo area, not relevant to cars.

- Option 2, bonnet: Known as the hood in American English, it covers the engine compartment of a car.

- Option 3, chassis: The correct term for the base frame of a wheeled vehicle, including cars.

- Option 4, cockpit: This is the area where the pilot sits in an aircraft, not related to cars.