前提结论结构的疑惑

yyujje

OG13-112：The difficulty with the proposed high-speed train line is that a used plane can be bought for one-third the price of the train line, and the plane, which is just as fast, can fly anywhere. The train would be a fixed linear system, and we live in a world that is spreading out in all directions and in which consumers choose the free-wheel systems (cars, buses, aircraft), which do not have fixed routes. Thus a sufficient market for the train will not exist.
Which of the following, if true, most severely weakens the argument presented above?
(A) Cars, buses, and planes require the efforts of drivers and pilots to guide them, whereas the train will be guided mechanically.
(B) Cars and buses are not nearly as fast as the high-speed train will be.
(C) Planes are not a free-wheel system because they can fly only between airports, which are less convenient for consumers than the high-speed train’s stations would be.
(D) The high-speed train line cannot use currently underutilized train stations in large cities.
(E) For long trips, most people prefer to fly rather than to take ground-level transportation.
  这道题的结构应该是前提结论结构吧。前提是飞机比火车省成本且速度一样，乘客喜欢包括飞机在内的free-wheel systems而不是火车这样的fixed linear system。 结论是火车将没有市场。 答案是C，说飞机不是free-wheel system，且不必火车便利。我的疑问是如果该题是前提结论结构，前提应该是默认为正确的，不应该被拿来驳斥的，所以不能批驳说飞机不是free-wheel system。还是说该题不是前提结论结构？或者前提指的另有其它？