TravelCheap Inc. is a car rental business that charges customers based on how many miles they put on a car on a daily basis. As result, a person who uses a car to travel from Chicago to Denver during a week is charged much more than a person who uses a car only to travel one mile to the grocery store six times a week.
TravelCheap uses a business model called:

A. freemium.
B. pay-as-you-go.
C. agency.
D. bundling.