If, at the Current Level of Output, the Extra Revenue

If, at the current level of output, the extra revenue received from producing and selling the last unit of output is less than the extra cost of producing that output, the firm should

A) expand rapidly.
B) expand cautiously.
C) do nothing.
D) reduce output to the point where the extra revenue is less than the extra cost.
E) reduce output to the point where the extra revenue just equals the extra cost.