Which of the following statements BEST describes a preaction sprinkler system?

A. Causes all sprinklers to discharge water simultaneously
B. Releases air when sprinkler activates, allowing the system to be charged with water
C. Continually charged with water under pressure that discharges when one or more sprinklers are activated by heat from a fire
D. Operates only when a sprinkler opens and a detection device in the same area activates the water-flow control valve

D