Which of the Following Is a Difference Between a Perfectly

Which of the following is a difference between a perfectly competitive market and a monopoly?

A) There are huge barriers to entry in a perfectly competitive market, while there are no barriers to entry in a monopoly.
B) Sellers in a perfectly competitive market are price-makers, while a seller in a monopoly market is a price-taker.
C) The equilibrium price in a perfectly competitive market exceeds marginal revenue, while the equilibrium price in a monopoly equals marginal revenue.
D) The market demand curve faced by a perfectly competitive firm is horizontal, while the market demand curve in a monopoly is downward-sloping.