Cassie is going to join a gym because new membership is very cheap. When she gets there, she discovers that there are added costs for towels, classes, and lockers. Although the final price is much higher than she originally believed, she still signs up. The gym has just used the __________ strategy to get Cassie to buy a membership.

a. normative influence
b. door-in-the-face
c. foot-in-the-door
d. lowballing