作为世界上最难的语法考试，GMAT对语法改错的考查早已超过语言知识本身，具有很强的综合性和很大的迷惑性。由于考查范围广、出错点多、原则多样化，虽然语法改错部分看起来容易把握，但在实际解题过程中，考生经常顾此失彼，在几个选项间徘徊犹豫半天依然难以确定最终答案。GMAT语法改错的难度一方面来自题干，另一方面来自选项，因为我们要依靠选项之间的差别来获得信息、寻求提示，其实这就反映了GMAT语法改错答案的特点——矮子里拔将军，也就是需要我们善于运用排除法，挑选出相对准确而有效的那一个。下面我们通过几个例子深入体会一下。

1. Acid rain and snow result from the chemical reactions between industrial emissions of sulfur dioxide and nitrogen oxides with atmospheric water vapor to produce highly corrosive sulfuric and nitric acids.

（A）with atmospheric water vapor to produce highly corrosive sulfuric and nitric acids

（B）with atmospheric water vapor producing highly corrosive sulfuric and nitric acids

（C）and atmospheric water vapor which has produced highly corrosive sulfuric and nitric acids

（D）and atmospheric water vapor which have produced sulfuric and nitric acids which are highly corrosive

（E）and atmospheric water vapor to produce highly corrosive sulfuric and nitric acids

这道题目的考查对象为between…and…这一常见的固定搭配，用来连接两个名词或名词短语，本题对考生的干扰主要在于sulfur dioxide和nitrogen oxides中间已经出现了一个and，有些考生就想到GMAT语法要求句子简明，那么连用and肯定不合适，首先将C，D和E排除掉了。但是如果用with，整句话逻辑关系不通，这个错误当然要比用词重复严重得多，相比之下还是选择使语意合乎逻辑的选项，正确答案为E。我们不选C和D的理由并不是由于句子不简洁，而是其逻辑关系有误。

2. A majority of the international journalists surveyed view nuclear power stations as unsafe at present but that they will，or could，be made sufficiently safe in the future.

（A）that they will，or could,

（B）that they would，or could,

（C）they will be or could,

（D）think that they will be or could

（E）think the power stations would or could 

题干中的but表转折关系，在对选项进行比较时A，B，C比较容易吸引考生眼球，因为它们与划线句相似，D和E凭空多出个think，让人感觉难以接受，但是如果仅仅以这个理由进行排除显然是证据不足的。我们应该先分析原句结构，抓住主线，该句属于平行结构形式，D和E中的think与view在意思上形成对应，所以我们不应对这两个答案带有任何偏见，而应一视同仁。根据GMAT语法原则，不能随意省略成分，否则句意就会出现ambiguity。比较五个选项，只有D的句意表达最完整。而为什么要使用think一词我们大可不必去追究，这只是无关痛痒的小问题。

3. Unlike the acid smoke of cigarettes, pipe tobacco, cured by age-old methods, yields an alkaline smoke too irritating to be drawn into the lungs.

(A) Unlike the acid smoke of cigarettes, pipe tobacco, cured by age-old methods, yields an alkaline smoke

(B) Unlike the acid smoke of cigarettes, pipe tobacco is cured by age-old methods, yielding an alkaline smoke

(C) Unlike cigarette tobacco, which yields an acid smoke, pipe tobacco, cured by age-old methods, yields an alkaline smoke

(D) Differing from cigarettes’ acid smoke, pipe tobacco’s alkaline smoke, cured by age-old methods, is

(E) The alkaline smoke of pipe tobacco differs from cigarettes’ acid smoke in that it is cured by age-old methods and is

解答本题时首先排除的是D答案，因为differ from不能用在句首。本题的正确答案为C，但是很多考生的目光都是在C上暂作停留就转向其他选项了。原因是C中连用了两个yield，这样的句子毫无美感可言，缺乏变化。可是千万别忘记考虑到句子重心问题，其他几个答案都是把句子重心搞错了，smoke和cigarette对应有误，这可是大禁忌，比起这个错误来，用词重复还算得了什么呢？

综上所述，选择GMAT语法改错答案时我们应牢记“没有最好，只有更好”，很少有一个答案是完美的，可以面面俱到的，我们所要选择的是相对来说错误最小的，最能清楚有效表达句意的。