what is the difference between marginal cost and marginal revenue?

A.) marginal cost is the money earned from selling one more unit of a good. marginal revenue is the money paid for producing one or more unit of good.
B.) marginal cost is the money paid for producing one more unit of a good. marginal revenue is the money earned from selling one more unit of a good.
C.) marginal cost is the money a producer might make from one more unit. Marginal revenue is the money a producer actually makes from one more unit
D.) marginal cost is the money a producer actually makes from one more unit. Marginal revenue is the money a producer might make from one more unit.