Perfectly competitive firms differ from monopolies in which of the following ways?
Perfectly competitive firms do not have to worry about the price effect lowering their total revenue. {Think of whether price effect plays a role if the price does not change.}
Marginal revenue for a perfectly competitive firm equals price, while marginal revenue for a monopoly is less than the price it is able to charge.
Monopolies must lower their price in order to sell more of their product, while perfectly competitive firms do not.