One Reason Why the Long-Run Supply Curve May Slope Upward

Multiple Choice

One reason why the long-run supply curve may slope upward in a competitive market is that

A) firms can exit the industry easily.
B) firms can enter the industry easily.
C) there are many buyers and many sellers.
D) some resources necessary to produce the product may be available only in limited supplies.
E) some resources necessary to produce the product are not limited.