Which of the following statements correctly describes the role that easy entry and exit play in competitive markets over the long run?
a)Entry and exit of firms is nonexistent in the long run.
b)Entry and exit of firms allows firms to earn an economic profit in the long run.
c)Entry and exit are important in the long run because firms need competition from other firms to remain in business.
d)As a result of entry and exit, firms earn a normal profit in the long run.