Answer: D. marginal revenue is affected by adding one additional unit sold at the new price.
Explanation:
Marginal Revenue is the amount that a firm gets for selling an additional unit of a good.
That means that if a monopolist increases their output by 1 unit and then sells that unit at a lower price, their Marginal Revenue increases by the sales amount of the 1 unit of the latest good that was just sold.
For example, they sell a good for $5 even though they had been selling at $6, Marginal Revenue would increase by $5.