Answer;
D. Smallest chunk
A unit of sale is the smallest chunk that a person can buy a product or service in.
Explanation;Unit sales measures the total amount of revenue that a product generates divided by the total number of units of that product that were sold in a given period. Unit sales are used by firms to determine the profitability of a certain product and also to improve, expand or cancel the product. It may also be used to determine the changes in demand.