Answer:
D. Natural Monopoly
Step-by-step 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.