The Usefulness and Relative Simplicity of the Supply and Demand

The usefulness and relative simplicity of the supply and demand model is often used

A) because nearly every major industry in the U.S. is governed by perfect competition.
B) because nearly every major industry in the U.S. is governed by monopoly.
C) even though, strictly speaking, few industries in the U.S. are governed by perfect competition.
D) even though it has no connection to economic reality.