GMAT邏輯中的“加強”思路小議

GMAT邏輯（Critical Reasoning）中的“加強”（strengthen）指的是正確選項為題干中的前提或結論提供支持，或強化從前提到結論的推斷過程，從而使得結論成立的可能性得以提高。典型的加強題如下：

　　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.

　　從題干中的but Rubco executives claim that不難判斷，本題的結論就是winning the bid will actually make a profit for the company。A項中的make and model與題目無關；B項提及a number of other models，但本題只討論Max 100一種車型；C項中的are located very near each other無助于得出make a profit的結論；E項中的price即使真的能使公司贏得合同，也無法證明盈利。而D項中的replace it with a part of exactly the same make and type意味著消費者很可能購買更多的tires，從而加強了結論。

　　值得注意的是，“加強”這種思路的存在遠不止于加強題，事實上GMAT邏輯中還有多種題型都可以看做是加強題的變種，如下例的解釋題：

　　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.

　　解釋題的特征是題干中存在不合常理的矛盾，需要加以解釋，換言之正確選項應當能夠加強那個看似不合理的結論。A項中的nutrients顯然無法加強這個結論，因為即使土壤的營養(yǎng)成分再適合grazing，也無法解決固有的盈利問題；B項所涉及的兩種climates的對比與題目無關，因為題目的討論范圍僅限于tropical Amazon forest；C項中的are more heavily taxed反而起到了削弱（weaken）作用；D項中的are killed by wildcats與盈利問題無關。而E項中的啟動資金數(shù)額巨大的問題，對應題干中的limited funds，很好的加強和解釋了結論。