In Which of the Following Situations Does an Exchange NOT

In which of the following situations does an exchange NOT occur?

A) Carlos pays Mrs. Smith $10 an hour to tutor him in English.
B) Morris mows Mr. Carpenter's yard in return for Mr. Carpenter's repair of his wife's sewing machine.
C) Tiffany buys a candy bar from a vending machine.
D) Hudson High School buys new football cleats for its team.
E) Before making a purchase, Eva evaluates the features and benefits of alternative brands.