GMAT邏輯推斷題兩招搞定

推斷題在GMAT邏輯中算是入門題型，它要求你承認文本中給出的信息均為真，此時能夠推出哪一個選項，提問形式有 “which of the following inferences is best supported by the passage” 或 “if the statements above are true, then which one of the following must also be true” 等。但對于剛接觸GMAT邏輯的同學而言，還是會因長句難懂、時間不夠等原因選錯答案。舉例如下：

People tend to estimate the likelihood of an event's occurrence according to its salience; that is, according to how strongly and how often it comes to their attention. By placement and headlines, newspapers emphasize stories about local crime over stories about crime elsewhere and about many other major events.

It can be concluded on the basis of the statements above, if they are true, which of the following is most probably also true?

(A) The language used in newspaper headlines about local crime is inflammatory and fails to respect the rights of suspects.
　　(B) The coverage of international events in newspapers is neglected in favor of the coverage of local events.
　　(C) Readers of local news in newspapers tend to overestimate the amount of crime in their own localities relative to the amount of crime in other places.
　　(D) None of the events concerning other people that are reported in newspapers is so salient in people's minds as their own personal experiences.
　　(E) The press is the news medium that focuses people's attention most strongly on local crimes.

文本信息用了兩句話，共50詞；提問和選項有130詞。這么長的題目，考試要求是兩分鐘內(nèi)選出答案。對考生而言這是何等的殘酷�，F(xiàn)在就來教大家兩招，在短時間內(nèi)盡量提高正確率，甚至直接做出答案。

1. 無關(guān)詞排除法

推斷題是一個對討論范圍要求非常嚴格的題型。由于正確選項由給出的信息推知，因此選項中討論的內(nèi)容必須來自給出的信息，不能隨性往外延伸。比如原文只說蘋果營養(yǎng)豐富，你就不能說香蕉營養(yǎng)豐富或蘋果口感很棒。如：

Experienced pilots often have more trouble than novice pilots in learning to fly the newly developed ultralight airplanes. Being accustomed to heavier aircraft, experienced pilots, when flying ultralight craft, seem not to respect the wind as much as they should.

The passage implies that the heavier aircraft mentioned above are

(A) harder to land than ultralight aircraft
　　(B) not as popular with pilots as ultralight aircraft
　　(C) not as safe as ultralight aircraft
　　(D) more fuel-efficient than ultralight aircraft
　　(E) easier to handle in wind than ultralight aircraft

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如果我們看選項時有意識地用上無關(guān)詞排除法，我們很快發(fā)現(xiàn)ABCD四個選項中的land（著陸）、popular（受歡迎與否）、safe（安全性）、fuel-efficient（燃油經(jīng)濟性）均未在原文中有任何相關(guān)的提及，故全部排除，只能選E。

2. 公共元素連接法

原文給出的幾句信息中（特別是兩句），如果有公共元素，我們可以把公共元素拿掉，再把剩下的東西拼在一起，讓剩下的東西產(chǎn)生聯(lián)系，很有可能就是正確答案。如“所有老師都放假。我是老師。”拿掉公共元素“老師”，結(jié)論就是“我放假”。

Increase in the level of high-density lipoprotein (HDL) in the human bloodstream lower bloodstream-cholesterol levels by increasing the body’s capacity to rid itself of excess cholesterol. Levels of HDL in the bloodstream of some individuals are significantly increased by a program of regular exercise and weight reduction.

Which of the following can be correctly inferred from the statements above?

(A) Individuals who are underweight do not run any risk of developing high levels of cholesterol in the bloodstream.
　　(B) Individuals who do not exercise regularly have a high risk of developing high levels of cholesterol in the bloodstream late in life.
　　(C) Exercise and weight reduction are the most effective methods of lowering bloodstream cholesterol levels in humans.
　　(D) A program of regular exercise and weight reduction lowers cholesterol levels in the bloodstream of some individuals.
　　(E) Only regular exercise is necessary to decrease cholesterol levels in the bloodstream of individuals of average weight.

這一題原文有兩句話，第一句講到HDL和bloodstream cholesterol的關(guān)系，第二句講到HDL和exercise and weight reduction的關(guān)系。兩句話的公共元素就是HDL，因此正確選項應(yīng)該要讓去掉公共元素后剩下的bloodstream cholesterol和exercise and weight reduction產(chǎn)生聯(lián)系。據(jù)此來看，正確選項應(yīng)該是D。

需要注意的是，這兩個方法本身并非相互排斥、非此即彼，我們在做題時可以把這兩個方法結(jié)合起來，讀完原文和提問知道是推斷題后，可以自己根據(jù)公共元素連接法構(gòu)想出一個大致的正確答案，再把無關(guān)詞排除法運用在篩選選項的過程中。

現(xiàn)在我們在回過頭來看第一個例子。原文還是兩句話，第一句話講的是“人們認為的一件事情發(fā)生的可能性的高低”與“這件事情的salience——被提及的強度與頻率”的關(guān)系，第二句話講的是“報紙總是報道本地犯罪的新聞”。

咋一看，似乎并沒有公共元素，其實第一句的“高salience”就是第二句的“總是報道”，或者說原文的詞組emphasize A over B，因此取出公共元素后的正確選項應(yīng)該把“人們認為的一件事情發(fā)生的可能性的高低”與“本地犯罪”結(jié)合，即人們認為本地犯罪發(fā)生的可能性很高。

然后我們再去篩選選項：A項的language明顯是無關(guān)詞；B項的international events有點像無關(guān)詞，但原文講到過elsewhere，先保留；C項符合我們的預估；D項personal experiences為無關(guān)詞；E項的most strongly語氣過分絕對，回文一看未有此意。比較B和C，B的neglect含義也過頭了，C最正確。

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