The Law of Diminishing Marginal Returns

The law of diminishing marginal returns

A) requires that all inputs be varied proportionately.
B) states that as an input is increased (all other inputs held constant) , total output falls after some point.
C) is relevant only when there is significant unemployment in the economy.
D) states that if more and more of a resource is used (the quantities of other resources being held constant) , after some point, the average, marginal, and total products all become equal.
E) states that as a variable input is increased (with other inputs remaining constant) , beyond some point the marginal product of the variable input falls.