Which of the following holds true? 

Select one: 

a. When MP is rising, MC is constant, and when MP is falling, MC is negative. 

b. When MP is rising, MC is falling, and when MP is falling, MC is rising. 

c. When the Marginal Product (MP) is rising, Marginal cost (MC) is rising; and when MP is falling, MC is falling. 

d. There is no relationship between MP and MC.