The four types of automatic sprinkler systems are:

• A. Wet-pipe systems, dry-pipe systems, deluge systems, and preaction systems.
• B. Automatic sprinkler systems, fixed sprinkler systems, Factory Mutual Systems, and UL listed systems.
• C. Wet sprinkler systems, deluge systems, Fire Mutual Systems, and hazardous substance systems.
• D. Water sprinkler systems, pneumatic sprinkler systems, flooding sprinkler systems, and chemical sprinkler systems.

Answer: (A)

The main idea is the standard way sprinkler pipes are filled and discharged water, which distinguishes four common automatic sprinkler system types: wet-pipe, dry-pipe, deluge, and preaction. Wet-pipe systems have water-filled pipes so any activated head releases water immediately. Dry-pipe systems keep the pipes dry with just air or an inert gas, and water is released into the pipes after a valve is opened, which helps prevent freezing. Deluge systems have all sprinkler heads open to water, so when the system is activated, water is discharged from every head. Preaction systems require a preliminary action (like a detection signal) to release water into the pipes, providing an extra safeguard against accidental discharge.

The other options mix in terms that aren’t standard types of sprinkler systems—things like fixed or pneumatic systems, or references to organizations and listings—so they don’t describe the categories used to classify automatic sprinkler systems.