What defines a dual air brake system?

Answer: C — Two brake systems and one set of controls

A dual air brake system is characterized by having two separate brake systems that operate independently, yet they share a single set of controls. This design enhances safety by providing a backup system; if one system fails, the other can still provide stopping power. In a dual system, each brake circuit usually operates on different parts of the vehicle, which minimizes the risk of complete brake failure. This system is crucial in commercial vehicles as it ensures that even in the event of a malfunction in one brake system, the driver can still control the vehicle safely using the other system. The redundancy provided by the dual air brake system is an important aspect of vehicle safety standards, particularly for larger vehicles that require reliable stopping capabilities.