An air brake is made up of which of the following braking systems?

Air brakes are really three different braking systems: service brake, parking brake, and emergency brake.
The service brake system applies and releases the brakes when you use the brake pedal during normal driving.
The parking brake system applies and releases the parking brakes when you use the parking brake control.
The emergency brake system uses parts of the service and parking brake systems to stop the vehicle in a brake system failure.
(According to CDL Handbook)