If the Marginal Social Benefit of a City's Sewage System

If the marginal social benefit of a city's sewage system is less than the marginal social cost, then the city will achieve an efficient use of resources if it

A) decreases the capacity of the sewage system.
B) does not change the capacity of the sewage system.
C) increases the capacity of the sewage system.
D) increases the sewerage charge that the residents pay.