In Order to Maximize Its Profit,or Minimize Its Loss,the Firm

In order to maximize its profit,or minimize its loss,the firm must hire workers until

A) the extra revenue from the last worker equals the extra profit.
B) the extra revenue from the last worker equals the extra cost.
C) total revenue and total labour cost are equal.
D) the marginal product of workers begin to decline.
E) the marginal product of workers becomes negative.