请牛牛们来解答~两道prep逻辑题的对比，疑惑啊！

ornello

请看一下prep8出现的两道逻辑题：

Q4.       p1-cr    55.        (34557-!-item-!-188;#058&007575)

Accordingto the Tristate Transportation Authority, making certain improvements to themain commuter rail line would increase ridership dramatically.  The authority plans to finance theseimprovements over the course of five years by raising automobile tolls on thetwo highway bridges along the route the rail line serves.  Although the proposed improvements are indeedneeded, the authority's plan for securing the necessary funds should berejected because it would unfairly force drivers to absorb the entire cost ofsomething from which they receive no benefit.

Which ofthe following, if true, would cast the most doubt on the effectiveness of theauthority's plan to finance the proposed improvements by increasing bridgetolls?

(A)Before the authority increases tolls on any of the area bridges, it is requiredby law to hold public hearings at which objections to the proposed increase canbe raised.

(B)Whenever bridge tolls are increased, the authority must pay a privatecontractor to adjust the automated toll-collecting machines.

(C)Between the time a proposed toll increase is announced and the time theincrease is actually put into effect, many commuters buy more tokens than usualto postpone the effects of the increase.

(D)（正确答案） Whentolls were last increased on the two bridges in question, almost 20 percent ofthe regular commuter traffic switched to a slightly longer alternative routethat has since been improved.

(E) Thechairman of the authority is a member of the Tristate Automobile Club that hasregistered strong opposition to the proposed toll increase.

Q21.    p1-cr    59.        (34753-!-item-!-188;#058&007583)

Acertain mayor has proposed a fee of five dollars per day on private vehiclesentering the city, claiming that the fee will alleviate the city's trafficcongestion.  The mayor reasons that,since the fee will exceed the cost of round-trip bus fare from many nearbypoints, many people will switch from using their cars to using the bus.

Which ofthe following statements, if true, provides the best evidence that the mayor'sreasoning is flawed?

(A)Projected increases in the price of gasoline will increase the cost of taking aprivate vehicle into the city.

(B)（正确答案） The cost of parking fees already makes it considerablymore expensive for most people to take a private vehicle into the city than totake a bus.

(C) Mostof the people currently riding the bus do not own private vehicles.

(D) Manycommuters opposing the mayor's plan have indicated that they would ratherendure traffic congestion than pay a five-dollar-per day fee.

(E)During the average workday, private vehicles owned and operated by peopleliving within the city account for twenty percent of the city's trafficcongestion.

我不理解的是为何Q21的（E）不正确？如果是因为20%太少了，不能影响结论，那么Q4正确选项的20%也不能有效的削弱呀？
还是因为Q4的其它选项更烂？
还有几天就考啦，竟然还在纠结选项。。。请NN们解答~

ornello

自己顶！

alzn2765

第一题是方案推理：
目的：to finance these improvements over the course of five years
正确答案是一个会使目的无法达到的情况。
D就是这个情况：其实就是个数学关系式 funds=additional charge x no. of cars pass by

第二题不是方案推理，是因果推理找削弱。
前提（因）：the fee will exceed the cost of round-trip bus fare from many nearb ypoints（使进城成本提高）
结论（果）： the fee will alleviate the city's traffic congestion（方案有效）

A--->B

削弱：
A--->B的有效否定是A交非B（逻辑基础，推理的有效否定式）
在B选项中：
A：The cost of parking fees already makes it considerablymore expensive for most people to take a private vehicle into the city than to take a bus（等同于使进城成本提高）
非B：the city's traffic congestion(现在的状态)

这就是A交非B的削弱。基础是逻辑基本理论基础。

D选项陈述一般事实，没有起到削弱作用。至于20%根本与削弱无关。

ornello

alzn2765 发表于 2015-8-6 11:31
第一题是方案推理：
目的：to finance these improvements over the course of five years
正确答案是一个 ...

太谢谢啦！我太关注于20%，没有注意到问题实质！A交非B是个新概念，想再请教一下，这个方法具体怎么在选项中应用呀？A是premise，B是结论，若选项=A交非B，就是有效否定？

alzn2765

ornello 发表于 2015-8-8 01:46
太谢谢啦！我太关注于20%，没有注意到问题实质！A交非B是个新概念，想再请教一下，这个方法具体怎么在选 ...

逻辑基础理论。

哎。。。CDer真的是被各种xx天7XX分冲昏头脑了，学习CR竟然都不看逻辑基础理论。。。
找本逻辑基础的书看看

ornello

alzn2765 发表于 2015-8-8 10:11
逻辑基础理论。

哎。。。CDer真的是被各种xx天7XX分冲昏头脑了，学习CR竟然都不看逻辑基础理论。。。

我只是学了powerscore和曼哈顿，没有想到要学逻辑基础。。。不过学习基础肯定对做题有很大帮助，谢谢你的回复啦！