The Marginal Product of Labor Is The

The marginal product of labor is the:

A) output which it could produce unaided by machinery or other factors of production.
B) extra revenue which a firm will get by selling the output of one additional worker.
C) amount of extra output that is produced when one extra worker is added to a fixed amount of other factors.
D) amount of extra output that is produced when one worker is added and other factors of production are increased proportionately.
E) none of the above.