The Marginal Revenue Curve of a Monopoly Firm Lies Below

The Marginal Revenue curve of a monopoly firm lies below the demand curve because:

A) in order to increase output the firm must lower its price, which means it receives less for the units already sold
B) as output increases the firm will need to sell to those who have a lower willingness-to-pay
C) monopolies are often regulated by governments that put limits on market prices
D) the monopoly must lower its price in order to discourage new firms from entering the market