In Order to Maximize Its Profits, a Firm That Hires

In order to maximize its profits, a firm that hires workers in a perfectly competitive labor market will hire workers until the:

A) extra revenue generated from hiring another worker equals the extra profit from hiring that worker.
B) extra revenue generated from hiring another worker equals the extra cost of hiring that worker.
C) the marginal wage rate equals marginal product of the last worker.
D) the marginal product of labor begins to decline.