An increase in demand for a monopolist will cause the

a) profit-maximizing price to decrease when marginal cost decreases as quantity increases.

b) profit-maximizing price to increase when marginal cost decreases as quantity increases.

c) profit-maximizing price to decrease when marginal cost increases as quantity increases.

d) profit-maximizing price to stay constant regardless of the shape of the marginal cost curve

The answer is A. Why?