Which one of the following is not the assumption of the Marginal Productivity Theory of Distribution?

Q.       Which one of the following is not the assumption of the Marginal Productivity Theory of Distribution?

A.           Homogeneity of a factor      

B.            Perfect competition in the factor market

C.            All factors, except one, are variable

D.           Given stock of each factor and full employment

Answer: All factors, except one, are variable