做weaken题，只能反对他的结论，不能反对前提，对吗？

OG109. Recently a court ruled that current law allows companies to reject a job applicant if working in the job would entail a 90 percent chance that the applicant would suffer a heart attack. The presiding judge justified the ruling, saying that it protected both employees and employers. 削：IF发生不了

The use of this court ruling as part of the law could not be effective in regulating employment practices if which of the following were true?

(A) The best interests of employers often conflict with the interests of employees. —>说的不是ruling本身有问题而不能实现（只是有时justification for ruling会unavailable）

(B) No legally accepted methods exist for calculating the risk of a job applicant’s having a heart attack as a result of being employed in any particular occupation. —>if发生不了的时候

(C) Some jobs might involve health risks other than the risk of heart attack. —>可能将来会有类似的其它ruling，但与此ruling是否有效无关

(D) Employees who have a 90 percent chance of suffering a heart attack may be unaware that their risk is so great. —>说的是applicant不是已有的雇员 B

(E) The number of people applying for jobs at a company might decline if the company, by screening applicants for risk of heart attack, seemed to suggest that the job entailed high risk of heart attack. —>只说明ruling对劳工市场可能有的非直接影响，但与ruling本身有无效果无关

The ruling would be ineffective in regulating employment practices if it could never be used to justify rejecting some application. According to choice B the ruling cannot be applied in a legally acceptable way. Thus choice B is the best answer.

二、OG中也有直接削前提的例子：

96.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. —>前提：因为飞机要比火车方便，结论：所以火车没市场；削：飞机不比火车更方便

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. —>此因素不会立即影响顾客的选择

(B) Cars and buses are not nearly as fast as the high-speed train will be. —>比的是飞机

(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. —>削前提：飞机不比火车更方便

(D) The high-speed train line cannot use currently underutilized train stations in large cities. —>加强 C

(E) For long trips, most people prefer to fly rather than to take ground-level transportation. —>加强

The author argues that planes, since they are a free-wheel system, will be preferred to the high-speed train. Choice C weakens the argument by pointing out that planes are not a free-wheel system and are less convenient than the high-speed train would be. Thus C is the best answer.

170. The proposal to hire ten new police officers in Middletown is quite foolish. There is sufficient funding to pay the salaries of the new officers, but not the salaries of additional court and prison employees to process the increased caseload of arrests and convictions that new officers usually generate. --前提：加警力会增加成本开支，结论：不应该增加警力；削：加警力会阻目犯罪从而减少成本开支

Which of the following, if true, will most seriously weaken the conclusion drawn above?

(A) Studies have shown that an increase in a city’s police force does not necessarily reduce crime. —>研究理论加强

(B) When one major city increased its police force by 19 percent last year, there were 40 percent more arrests and 13 percent more convictions. —>别的城市例子证明确实会提高成本，加强

(C) If funding for the new police officers’ salaries is approved, support for other city services will have to be reduced during the next fiscal year. —>资金困难，加强

(D) In most United States cities, not all arrests result in convictions, and not all convictions result in prison terms. —>无关，仅仅说明了三者间明显的关系

(E) Middletown’s ratio of police officers to citizens has reached a level at which an increase in the number of officers will have a deterrent effect on crime. —>M城增加警力就能阻止犯罪，从而可能阻止更多的费用产生

The passage says that hiring new officers usually brings new court expenses, but according to choice E hiring new officers in Middletown will lead to a reduction in crime and thus, perhaps, a reduction in court and prison expenses. Therefore, choice E weakens the conclusion drawn and is the best answer.