单选题 Assume that a perfectly competitive firm produces 10 units of a good and sells them each for a price (P) equal to $15. If the marginal cost (MC) of the 10th unit is $15 and the average total cost (ATC) is $13, economic profit for the firm is closest to:

A、

A. $0.
B、

B. $130.
C、

C. $20.

【正确答案】 C

【答案解析】When MR=MC=P, economic profit equals TR-TC. In this case, TR=$150=10×$15 and TC=$130=10×ATC=10×$13. So, economic profit is $20=$150-$130.