Brand X Is One of Many Firms in a Competitive

Brand X is one of many firms in a competitive industry where each firm has a constant marginal cost of 2 dollars per unit of output. If marginal cost for Brand X rises to 4 dollars per unit and marginal costs of all other firms in the industry stay constant, by how much does the price in the industry increase?

A) 2 dollars
B) 1 dollar
C) 0 dollar
D) 2/n , where n is the number of firms in the industry
E) None of the above.