Regulation May Be Important in an Industry with Significant Economies

Regulation may be important in an industry with significant economies of scale because:

A) only regulated sellers are allowed to exploit economies of scale.
B) without regulation, economies of scale would cause a firm's long-run average total cost curve to increase.
C) economies of scale may give rise to a natural monopoly that produces efficiently but could abuse its monopoly power.
D) all of the above.