21. In the short run, if there is an increase in industry demand in a purely competitive industry

A) Additional firms will enter the industry and industry output will expand

B) The market price will tend to rise, causing the representative firm to expand its output

C) The demand curve facing the representative firm will shift upward, causing it to cut back on output.

D) The market price will tend to fall, causing the representative firm to reduce its output

E) The market price will be unchanged, but the representative firm will tend to expand its output.