In any production process， the marginal product of labor equals：

A.the value of total output minus the cost of the fixed capital stock.

B.the change in output per unit change in labor input for '；small'； changes in the amount of input.

C.total output divided by total labor inputs.

D.total output produced with the given labor inputs.

正确答案：the change in output per unit change in labor input for '；small'； changes in the amount of input.