A Bridge Becomes Congested After 100 Vehicles Per Hour Use

A bridge becomes congested after 100 vehicles per hour use it on any day.To achieve efficiency, a toll:

A) that charges all users of the bridge, no matter how many vehicles use it per hour, should be imposed.
B) on additional users in excess of 100 per hour should be imposed.
C) on all users should be imposed, if more than 100 users per hour are expected.
D) is not required.