In the Long Run in a Competitive Market

In the long run in a competitive market,

A) existing firms can increase their plant size,and new firms can enter the market
B) existing firms can increase their plant size,but the number of firms is the market is fixed
C) new firms can enter the market,but existing firms cannot vary their plant size
D) new firms can enter the market,but only if existing firms decrease their plant size in the short run
E) existing firms can increase their plant size,only if some other firms exit