Which of the Following Best Expresses the Law of Diminishing

Which of the following best expresses the law of diminishing returns?

A) Because large-scale production allows the realization of economies of scale, the real costs of production vary directly with the level of output.
B) Population growth automatically adjusts to that level at which the average product per worker will be at a maximum.
C) As successive amounts of one resource (labor) are added to fixed amounts of other resources (capital) , beyond some point the resulting extra or marginal output will decline.
D) Proportionate increases in the inputs of all resources will result in a less-than-proportionate increase in total output.