Possible Benefits of a Monopoly Include Which of the Following

Possible benefits of a monopoly include which of the following (choose all that apply) ?

A) a savings of fixed costs because only one firm supplies quantity demanded.
B) greater opportunities for research due to long-run positive economic profits.
C) government regulation is more effective because the firm is "too big to fail."
D) goods and services are provided at a lower price than under perfect competition because of a monopoly's decreasing average cost curve.