The main difference between a monopoly and a perfectly competitive firm is that

A) a perfectly competitive firm creates deadweight loss, while a monopoly does not.

B) their cost curves are shaped differently.

C) a monopoly produces where P = MC, while a competitive firm produces where MR = MC.

D) perfectly competitive firms can change their levels of output, while monopolies cannot.

E) a monopoly is considered a price maker and a perfectly competitive firm is considered a price taker.