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：
In 2000, a mere two dozen products accounted for half the increase in
spending on prescription drugs, a phenomenon that is explained not just
because of more expensive drugs but by the fact that doctors are writing many more prescriptions for higher-cost drugs.
(A) a phenomenon that is explained not just because of more expensive drugs
but by the fact that doctors are writing
(B) a phenomenon that is explained not just by the fact that drugs are
becoming more expensive but also by the fact that doctors are writing
(C) a phenomenon occurring not just because of drugs that are becoming more
expensive but because of doctors having also written
(D) which occurred not just because drugs are becoming more expensive but
doctors are also writing
(E) which occurred not just because of more expensive drugs but because
doctors have also written
选项分析：
(A)a phenomenon that is explained not just because of more expensive drugs
but by the fact that doctors are writing
【错误】 平行结构：“but”两边应连接平行结构，而“because of……”和“by the fact
that……”虽然语法功能基本一致，但逻辑含义上并没有(B)中“by the fact that……”与“by the fact
that……”的平行结构更加对等。
(B)a phenomenon that is explained not just by the fact that drugs are
becoming more expensive but also by the fact that doctors are writing
【正确】 主谓结构的结尾加逗号再加名词性结构时，该名词性结构可以用来修饰其前面整个主谓结构。由“that”引导的定语从句修饰的名词“a
phenomenon”进一步修饰了其前面的主谓结构“a mere two dozen products accounted for half the
increase in spending on prescription drugs”，语法正确且语义合理。“not just by the fact
that……”和“by the fact that……”正确地用“but”平行在一起。
【大意】 2000年，区区24中产品可以解释处方药消费增长的一半，这一现象不仅可以被药变得更贵来解释，也可以被医生在开更贵的药来解释。
(C)a phenomenon occurring not just because of drugs that are becoming more
expensive but because of doctors having also written
【错误】 句子意思：本句后本部分的本意是“(现象)发生并不仅仅应为药品变得更贵而且因为医生开了高成本药品”，但“because of drugs that
are becoming more expensive”和“because of doctors having also written”是“because
of”引导的，分别以“drugs”和“doctors”为核心名词的结构，因此其表意实际上是“不仅因为变得更加昂贵的药品而且因为开了高成本药品的医生”，“原因”的重心落到了“药品”和“医生”上。
(D)which occurred not just because drugs are becoming more expensive but
doctors are also writing
【错误】 修饰成分：“，which resulted from an oversupply”本意上想修饰“a mere two dozen
products accounted
for……”这个主谓结构，然而在GMAT所考察的标准书面英语中。“，which……”只能做非限定性定语从句，即只能用来修饰一个名词性结构，不可以用来修饰一个主谓结构。
(E)which occurred not just because of more expensive drugs but because
doctors have also written
【错误】 修饰成分：见(D)。
解题思路：
“which”引导的从句在GMAT考察的标准书面英语中不能修饰之前的主谓结构，而只能修饰作为定语从句修饰名词性结构，立即排除(D)、(E)。
(A)、(B)和(C)中只有(B)合理使用了平行结构“not just by……but also by……”，且表意准确合理，因此选择(B)。
