Which of the following materials is considered flammable?

Gasoline is classified as a flammable material because it has a low flash point, meaning it can easily ignite and produce flammable vapors when exposed to an open flame or spark. This characteristic makes it a significant fire hazard, especially in environments where ignition sources may be present.

In contrast, water, concrete, and sand are not flammable. Water is an effective fire suppressant and is commonly used to extinguish fires. Concrete is a non-combustible material that does not burn or catch fire. Similarly, sand serves as a barrier to fire and can also be used to suffocate flames by covering combustibles, thus preventing ignition. These properties highlight the critical difference in fire risk between gasoline and the other materials listed.