Controllers include air-, __________ or electric- operated units.

• A. hydraulic-
• B. pneumatic-
• C. electrical-
• D. mechanical-

Answer: (A)

Controllers are categorized by how they are actuated, using different power sources to operate the mechanism. In fire pump and similar control systems, the common methods are air-operated (pneumatic), hydraulic-operated, and electric-operated. Since the statement already mentions air-, the natural third option to complete the trio is hydraulic-, which denotes actuation by fluid pressure. Hydraulic controllers provide strong, smooth actuation and are suited for components that require more force than pneumatic systems can easily deliver. The electric option is already included at the end, so it wouldn’t fit the middle slot, and mechanical is less typical for this standard classification.