Which of the following is NOT a common type of fire extinguishing agent?

The identification of plastic as not a common type of fire extinguishing agent is accurate because plastic is not a fire extinguishing material. Fire extinguishing agents are substances used to suppress fires effectively, and the common types include water, foam, and dry powder. Water is a primary agent for cooling, foam is used for suppressing flammable liquid fires, and dry powder agents are effective against a variety of fire classes, particularly metal fires.

Plastic, however, is a combustible material that can catch fire and does not have the properties necessary to combat or suppress a fire. Thus, it does not fit the criteria for being categorized as a fire extinguishing agent. This distinction is crucial for understanding the basic principles of fire suppression and the types of materials used in the firefighting process.