GMAT句子改错题(sentence correction)，是整个GMAT考试中对考生英语语法能力考查要求最高的题型，也往往是中国学生最为头疼的一类题目。没有扎实的语法基础和一定的逻辑分析能力，想要做好句子改错题难度极高。如何提升GMAT句子改错题的解题能力?下面小编就为大家整理了一些经典例题，结合实例分析为大家讲解GMAT句子改错题的解题思路和方法技巧。
实例题目：
Recently physicians have determined that stomach ulcers are not caused by stress, alcohol, or rich foods, but a bacterium that dwells in the mucous lining of the stomach.
(A) not caused by stress, alcohol, or rich foods, but
(B) not caused by stress, alcohol, or rich foods, but are by
(C) caused not by stress, alcohol, or rich foods, but by
(D) caused not by stress, alcohol, and rich foods, but
(E) caused not by stress, alcohol, and rich foods, but are by
选项分析：
(A)not caused by stress, alcohol, or rich foods, but
【错误】 平行结构：“but”两边应连接平行结构(语法功能一致，逻辑含义对等)，而本选项“but”两边 “a bacterium”和“not caused by stress, alcohol, or rich foods”语法功能不一致，因此无法平行。而“a bacterium”与“stress, alcohol, or rich foods”平行也不合理，因为本句的本意是“stomach ulcers”不是被“stress, alcohol, or rich foods”而是被“a bacterium”
引起，而如果仅把“a bacterium”与“stress, alcohol, or rich foods”用“but”平行，则表达的含义是“stomach ulcers” 不是被“stress, alcohol, or rich foods”但也不是被“a bacterium” 引起。
(B)not caused by stress, alcohol, or rich foods, but are by
【错误】 平行结构：“are not caused by”和“but are by”逻辑含义上不平行，后者没有“caused”。
(C)caused not by stress, alcohol, or rich foods, but by
【正确】 “not by stress, alcohol, or rich foods”和“by a bacterium that dwells in the mucous lining of the stomach”正确地用“but”平行在一起。
【大意】 最近内科医生认定，胃溃疡不是被焦虑、酒精或过量食物引起，而是被一种生活在胃黏膜上的细菌引起。
(D)caused not by stress, alcohol, and rich foods, but
【错误】 平行结构：类似地，见(A)中“平行结构”，语法结构上“a bacterium”只能和“stress, alcohol, and rich foods”平行，共同受到“caused not by”的影响，语义变为“stomach ulcers” 不是被“stress, alcohol, or rich foods”但也不是被“a bacterium” 引起。
(E)caused not by stress, alcohol, and rich foods, but are by
【错误】 平行结构：类似地，见(B)。
解题思路：
只有(C)正确使用“but”连接的平行结构，构成了“not X but Y”的平行句式，因此选择(C)。
