Which components are included in disc brakes?

The inclusion of calipers, pads, and rotors in disc brakes is essential to their functionality. The caliper serves as the component that houses the brake pads and is responsible for gripping the rotors when the brakes are applied. The pads are the friction material that presses against the rotors to create the necessary friction for stopping the vehicle. The rotors are the circular metal discs that the brake pads clamp down on, converting kinetic energy into thermal energy to slow down or stop the vehicle. This configuration is fundamental to how disc brake systems operate, making option A the correct answer.

In contrast, the other options mention various components that are not part of the disc brake system but rather belong to either drum brake systems or different aspects of the braking system. For instance, brake lines, drums, and shoes reference a drum brake system, while items like the master cylinder and vacuum booster pertain to hydraulic and power assistance features rather than the disc brake design itself.