Every time Beth buys a book at The Venus Bookstore, she presents her Venus card, and the sales associate enters her purchase in a database. When she has purchased five books at regular price, she is sent a coupon for a free book to be picked out on her next visit to the store. This is an example of a:
A. sweepstakes program.
B. premium promotion.
C. loyalty program.
D. customer rewards contest.
E. rebate program.