How Do Economies of Scale Contribute to the Development of an Oligopoly

Multiple Choice

How do economies of scale contribute to the development of an oligopoly?

A) Economies of scale make it legally difficult for new firms to enter.
B) Economies of scale make small-scale producers inefficient.
C) Economies of scale are based on control of a key resource, without which other firms cannot enter an industry.
D) Economies of scale are guaranteed when a patent is granted.