A firm will exit a competitive market when A. costs force the marginal cost curve to shift to the left. B. the longrun profit would be negative. C. it can earn only earn a zero longrun profit. D. Both B and C.

B. the longrun profit would be negative.

Explanation:

A perfect competition is characterized by many buyers and sellers of homogenous goods and services. Market prices are set by the forces of demand and supply. There are no barriers to entry or exit of firms into the industry.  

In the long run, firms earn zero economic profit.  If in the short run firms are earning economic profit, in the long run firms would enter into the industry. This would drive economic profit to zero.  

Also, if in the short run, firms are earning economic loss, in the long run, firms would exit the industry until economic profit falls to zero.  

A firm would shut down in the short run if price is less than average variable cost and exit if it  is making a loss

answercontrol is returned to method c;

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