Regarding a Producer's Cost Structure

Multiple Choice

Regarding a producer's cost structure:

A) marginal cost begins to rise at a lower level of output than average cost.
B) total fixed costs increase continuously as more units are produced.
C) average cost is the extra cost of producing one more unit.
D) average costs usually drop for awhile and then start to rise when the economies of scale "run out."
E) Both A and D are true.