When a single firm can supply a product to an entire market at a lower cost than could two or more firms, the industry is called a a. resource industry. b. exclusive industry. c. government monopoly. d. natural monopoly.

D. Natural Monopoly

Explanation:

Natural Monopoly occurs when a single firm can supply a product to an entire market at a lower cost than could two or more firms. A natural monopoly is based on economies of scale.

Economies of scale act as a barrier to entry because one large firm can produce the market output at a lower average cost than several small firms.

A natural monopoly is created by substantial economies of scale.

Natural monopoly is a type of monopoly that exists due to the high starts-up cost or powerful economies of scale.