The law of diminishing returns indicates that:

A.as extra units of a variable resource are added to a fixed resource, marginal product will decline beyond some point.

B.because of economies and diseconomies of scale a competitive firms long-run average total cost curve will be U-shaped.

C.the demand for goods produced by purely competitive industries is downsloping.

D.beyond some point the extra utility derived from additional units of a product will yield the consumer smaller and smaller extra amounts of satisfaction.