What is the A-pillar of a car?

The A-pillar of a car serves as the vertical support on either side of the windshield and connects the windshield to the vehicle's body. This structure is crucial for maintaining the integrity of the vehicle, providing strength and stability, especially in the event of a collision. It also is vital for the attachment of the front windows and plays a role in the overall aerodynamics of the vehicle.

The option relating to the separation of the windshield and side window correctly identifies the A-pillar's location and function within the car's design.