The key difference between taxi-style services and urban mass transit services is _____.
a. the dominance of cars alone in taxi-style services compared to the use of different modes in mass transit
b. the cost to the municipality; mass transit is more costly to municipalities
c. taxi services allow trip planning by the customer, while mass transit routes and schedules are planned by the transportation provider
d. the cost to the consumer; taxi-style services are most costly to individuals