A Monopoly Market Structure Is Characterized by

A monopoly market structure is characterized by

A) large number of firms, standardized products, easy entry and exit.
B) large number of firms, differentiated products, easy entry and exit.
C) small number of firms, standardized or differentiated products, difficult entry.
D) one firm, an unique product without close substitutes, and impossible entry.
E) one firm, differentiated product, impossible entry.