GMAT是一场知识积累的考验，也是一场逻辑思维的竞技，相信大家在“经年累月”备考的过程中对GMAT测试的知识点已经不陌生。然而，常言道“细节决定成败”，一些细微的考点也不容忽视。今天，小编就给大家分析一下GMAT SC中逗号的三种使用方法。

　　1.逗号不能连接两个句子。

　　eg：Charles Lindbergh. for his attempt at a solo transatiantic fight,was very reluctant to have any extra weight on his plane,he therefore refused to carry even a pound of mali,despite being offered ¥1000 to do so.

　　题干有两个完整的句子：

　　1.Charles Lindbergh was very reluctant to have any extra weight on his plane

　　2.he therefore refused to carry even a pound of mali

　　这两个句子中间必须有：

　　a. 连词：and，or，but，yet.

　　b. 从句引导词：although，because，when，while，since，etc.

　　注：however,therefore都是副词，并不能用来连接句子。

　　2. that/which前后有逗号的情况。

　　a. 一般情况下，that前不能加逗号。

　　eg: Based on accounts of various ancient writers，scholars have painted a sketchy picture of the activities of an all-female cult that,perhaps as early as the sixth century B.C.,worshipped a goddness known in Latin as Bona Dea,the good goddness.

　　b. that前面有逗号：that前有插入语。

　　eg: Scientists have found signs that moving water changed the chemical makeup of the surface of Mars in recent eras and concluded,therefore,that the planet·s crust is harboring up to three times more water as was previously thought.

　　3.and前后的逗号使用情况。

　　and前加逗号与否没有大的影响，但and后加逗号需注意。

　　eg：While they remove carbon dioxide from the air,conserve soil and water,and house thousands of species,forests also supply potentially valuable pharmaceuticals,and,as sources of building material and firewood,that provide employment for millions worldwide.

　　A. pharmaceuticals,and,as sources of building material and firewood,that provide

　　B. pharmaceuticals,and sources of building material and firewood,are providers of

　　C. pharmaceuticals and,as sources of building material and firewood that are pproviding

　　D. pharmaceuticals and sources of building material and firewood, for providing

　　E. pharmaceuticals and,as sources of building material

　　注：and后有逗号，需跳过插入语寻找平行