A case when internal economies of scale bring about a continuously falling average cost curve that makes having more than one firm in an industry inefficient is illustrative of ?

A case when internal economies of scale bring about a continuously falling average cost curve that makes having more than one firm in an industry inefficient is illustrative of ?

A. a natural monopoly
B. an LDC’s limit of one firm to an industry
C. an individual firm facing a horizontal (perfectly elastic) demand curve in LDCs
D. The existence of oligopoly