Which of the Following Is NOT an Example of a Retail

Which of the following is NOT an example of a retail activity?

A) A secretary orders airline tickets for her summer vacation.
B) A shoe store owner buys his wife a pair of sandals.
C) A contractor orders a skylight kit for a house she is contracted to build for a client.
D) A bookstore sells paperbacks to students at a book fair.
E) A member of the U.S. Olympic table tennis team buys himself an Olympic pin from a street vendor.