If a Firm Hires 200 Workers and Produces 5,000 Computers

If a firm hires 200 workers and produces 5,000 computers. If the firm hires one more worker, it produces 5,050 computers. If computers sell at a constant price of $100 and labor is hired at a constant wage rate of $4,000 per worker

A) the firm should hire and retain the additional worker.
B) the marginal factor cost of labor is $4,000.
C) the marginal revenue product of the added worker is $5,000.
D) all of the above.