If firms are making positive economic profits in the short run,then in the long run:

A) the short-run industry supply curve will shift leftward.
B) new firms will enter the industry.
C) industry output will rise and the price will rise.
D) firms will leave the industry.

When firms in an industry are making positive economic profits, it attracts new firms into the industry because they are attracted by the opportunity to earn profits. This entry of new firms increases the industry's output and typically leads to a decrease in prices until economic profits are normalized (i.e., reduced to zero).