If a Monopsonist Pays the Wage Rate W, Then the Amount

If a monopsonist pays the wage rate w, then the amount of labor that he can hire is L(w) = Aw, where A is a positive constant. The marginal cost of labor to the monopsonist is

A) equal to the wage rate.
B) twice the wage rate.
C) half the wage rate.
D) greater than the wage rate but less than twice as great.
E) less than the wage rate but more than half as great.