Final answer:
Class 3 is the DOT hazard class that includes flammable liquids.
Step-by-step explanation:
The DOT hazard class that includes flammable liquids is Class 3. Flammable liquids are substances that have a flashpoint below 100°F (37.8°C) and can ignite easily. Examples of flammable liquids include gasoline, ethanol, and acetone.