GMAT逻辑中的“加强”思路小议

GMAT逻辑（Critical Reasoning）中的“加强”（strengthen）指的是正确选项为题干中的前提或结论提供支持，或强化从前提到结论的推断过程，从而使得结论成立的可能性得以提高。典型的加强题如下：

　　The Maxilux car company’s design for its new luxury model, the Max 100, included a special design for the tires that was intended to complement the model’s image. The winning bid for supplying these tires was submitted by Rubco. Analysts concluded that the bid would only just cover Rubco’s costs on the tires, but Rubco executives claim that winning the bid will actually make a profit for the company.

　　Which of the following, if true, most strongly justifies the claim made by Rubco’s executives?

　　(A) In any Maxilux model, the spare tire is exactly the same make and model as the tires that are mounted on the wheels.
　　(B) Rubco holds exclusive contracts to supply Maxilux with the tires for a number of other models made by Maxilux.
　　(C) The production facilities for the Max 100 and those for the tires to be supplied by Rubco are located very near each other.
　　(D) When people who have purchased a carefully designed luxury automobile need to replace a worn part of it, they almost invariably replace it with a part of exactly the same make and type.
　　(E) When Maxilux awarded the tire contract to Rubco, the only criterion on which Rubco’s bid was clearly ahead of its competitors’ bids was price.

　　从题干中的but Rubco executives claim that不难判断，本题的结论就是winning the bid will actually make a profit for the company。A项中的make and model与题目无关；B项提及a number of other models，但本题只讨论Max 100一种车型；C项中的are located very near each other无助于得出make a profit的结论；E项中的price即使真的能使公司赢得合同，也无法证明盈利。而D项中的replace it with a part of exactly the same make and type意味着消费者很可能购买更多的tires，从而加强了结论。

　　值得注意的是，“加强”这种思路的存在远不止于加强题，事实上GMAT逻辑中还有多种题型都可以看做是加强题的变种，如下例的解释题：

　　Suncorp, a new corporation with limited funds, has been clearing large sections of the tropical Amazon forest for cattle ranching. This practice continues even though greater profits can be made from rubber tapping, which does not destroy the forest, than from cattle ranching, which does destroy the forest.

　　Which of the following, if true, most helps to explain why Suncorp has been pursuing the less profitable of the two economic activities mentioned above?

　　(A) The soil of the Amazon forest is very rich in nutrients that are important in the development of grazing lands.
　　(B) Cattle-ranching operations that are located in tropical climates are more profitable than cattle-ranching operations that are located in cold-weather climates.
　　(C) In certain districts, profits made from cattle ranching are more heavily taxed than profits made from any other industry.
　　(D) Some of the cattle that are raised on land cleared in the Amazon are killed by wildcats.
　　(E) The amount of money required to begin a rubber-tapping operation is twice as high as the amount needed to begin a cattle ranch.

　　解释题的特征是题干中存在不合常理的矛盾，需要加以解释，换言之正确选项应当能够加强那个看似不合理的结论。A项中的nutrients显然无法加强这个结论，因为即使土壤的营养成分再适合grazing，也无法解决固有的盈利问题；B项所涉及的两种climates的对比与题目无关，因为题目的讨论范围仅限于tropical Amazon forest；C项中的are more heavily taxed反而起到了削弱（weaken）作用；D项中的are killed by wildcats与盈利问题无关。而E项中的启动资金数额巨大的问题，对应题干中的limited funds，很好的加强和解释了结论。