Expand commuter rail system --> Reduce highway congestion.
To implement the plan, residents have to pay additional tax. --> Residents favored the plan --> Plan will succeed

Possible Weakener: If each resident thinks that others will use the commuter rail and favors to use the car, then the highway congestion will not reduce and the plan will fail.

A) it overlooks the possibility that once the highways are consistently uncongested, some commuters might have no motivation to switch from using their car to using the rail system. - Incorrect. This will reduce congestion on highways because some have motivation to use the rail system.

B) the favorable responses collected are entirely consistent with every one of those respondents expecting that it would be others who, by using the rail system, would ease highway congestion. - Correct

C) those respondents who opposed the plan might nevertheless become users of the rail system as a result of its expansion. - Incorrect - Strengthener

D) those respondents who opposed the plan might oppose it for reasons other than the tax increase required to carry it out. - Incorrect - Majority of Residents did not oppose the plan. So even if few residents oppose the plan, the plan will succeed. Not a weakener

E) residents responding to the poll are likely to overestimate the tax increase they themselves will experience if the proposed expansion occurs. - Incorrect - Out of context

Answer: B