What does a pneumatic control circuit primarily consist of?

A pneumatic control circuit primarily consists of a configuration of pneumatic components because these circuits are designed to use compressed air or gas to transmit and control energy. Pneumatic systems utilize specific components such as compressors, actuators, valves, and pressure regulators that work together to perform tasks such as moving machinery or controlling processes.

The primary focus is on the use of air or other gases in its entirety. These components are selected for their ability to harness pneumatic pressure, providing the necessary actuation and control within the circuit. The design and arrangement of these pneumatic elements determine how effectively the system will operate, reflecting the importance of properly configuring these components for the intended application. This makes option D the most accurate representation of what a pneumatic control circuit is comprised of.