For a pure monopolist,marginal revenue is less than price because:

A) the monopolist's demand curve is perfectly elastic.
B) the monopolist's demand curve is perfectly inelastic.
C) when a monopolist lowers price to sell more output,the lower price applies to all units sold.
D) the monopolist's total revenue curve is linear and slopes upward to the right.

A pure monopolist has market power and so can set the price of their product. However, in order to sell more units, the monopolist must lower the price on all units sold, hence the marginal revenue gained from selling an additional unit is less than the price. This is because the monopolist faces a downward-sloping demand curve, meaning that to sell more units, they must lower the price on all units, resulting in lower marginal revenue. Therefore, the answer is C.