Acartel differs from a monopoly in that
a. one corporation has complete control of a product or service.
b. businesses making the same product agree to limit production.
c. one firm sets the prices for all goods in an industry.
d. all the firms involved in the same business merge into one entity.

A cartel is different from a monopoly in that businesses making the same product agree to limit production - B

What usually happens during "cartelling" is that smaller businesses, or bigger ones as well, agree on setting the amount of goods that are to be produced lower and thereby controlling the flow of product availabity and with that money.