There are four classes of air systems.

• A. True
• B. False
• C. Depends on jurisdiction
• D. Not specified

Answer: (A)

In HVAC licensing material, air systems are typically grouped into four broad delivery configurations to capture the main ways conditioned air is supplied and circulated in buildings. This four-class framework is a common, widely taught convention, which is why the statement that there are four classes is considered true. While exact terminology can vary by code or region, the underlying idea is that there are four main categories, and exams use that standard framework to test your ability to recognize and compare different system layouts. The other options imply ambiguity or jurisdictional variation that isn’t how these exam materials are usually presented, so they don’t fit the standard four-class approach.