According to the Tristate Transpotation Authority, making certain improvements to the main commuter rail line would increase ridership dramatically.The authority plans to finance these improvements over the course of five years by raising automobile tolls on the two high-way bridges along the route the rail line serves.Although the proposed improvements are indeed needed, the authority's plan for securing the necessary funds should be rejected because it would unfairly force drivers to absorb the entire cost of something from which they receive no benefit.

which of the following, if true, would cast the most doubt on the effectiveness of the authority's plan to finance the proposed improvements by increasing  bridge tolls?
A, Before the authority increase tolls on any of the area bridges, it is required by law to hold public hearing at which objections to the proposed increase can be raised.
B, whenever bridge tolls are increased, the authority must pay a private contractor to adjust the automated toll-collecting machines.
C,Between the time a proposed toll increase is announced and the time the increase is actually put into effect, many commuters buy more tokens than usual to postpone the effects of the increase.
D, When tolls were last increased on the two bridges in question, almost 20 percent of the regular commuter traffic switched to a slightly longer alternative route that has since been improved.
E, The chairmen of the authority is a member of the Tristate Automobile Club that has registered strong opposition to the proposed toll increase.

The key is D.
为什么A不对呢。公共投票反对的话，那么这项提案不就不能实现吗？
请哪位大侠指点一下。谢谢了。