A monopolist faces a demand curve given by: P = 40 -Q, where P is the price of the good and Q is the quantity demanded. The marginal cost of production is constant and is equal to $2. There are no fixed costs of production. How much output should the monopolist produce in order to maximize profit?

A. 38 units.

B. 0 units.

C. 40 units.

D. 22 units.

E. None of these.