De Beers Has a Monopoly in the Market for Diamonds

De Beers has a monopoly in the market for diamonds because they own a significant portion of the known diamond mines. One important source of challenge to De Beers' control of the diamond market is

A) the additional market supply from Russia, Australia, and Canada
B) the emerging auction markets for diamonds in France and Spain
C) the growing demand for diamonds in industrial uses
D) that its South African mines are not producing as many diamonds as they did decades ago
E) antitrust legislation in the United States