平行结构是指用并列连词连接两个或两个以上的单词、短语或句子。平行结构是SAT语法常考的内容，有一定的规律可循。考生只要熟悉常见的表示平行结构的标志词，就可以迅速判断解题。

常见平行结构标志词：

平行结构中的成分A和B必须在语法形式上一致。例如：

1. She never drinks or smokes.

2. He walked across the street and into the school.

3. My sister is a dancer but her parents are teachers.

4. Jacob speaks slowly and clearly.

5. Prince William loves Kate Middleton not because of her beauty but because of her intelligence.

6. Seeing is believing. =To see is to believe.

7. Obama would either campaign for the president or campaign for the governor.

   Obama would campaign either for the president or for the governor.

   Obama would campaign for either the president or the governor.

例题讲解

1. To attempt acomprehensive mapping of the human genome is undertaking an extremelyambitious project.

1. genome is undertaking

2. genome is to undertake

3. genome undertakes

4. genome , it undertakes

5. genome, thus undertaking

解析：选B。根据平行结构句式Todo is to do，只有B选项满足这个平行结构的标准。A选项犯的是todo is doing这样的错误，不定式不能和动名词构成平行结构。C选项句意错误。D选项it指代不明，句意模糊。E选项句子结构不完整，没有谓语动词。

2. A fineorchestral performance will exhibit the skills of the musicians, their abilityto work as an ensemble and how he or she responds to the conductor.

1. how he or she responds

2. how to respond

3. their responding

4. their responses

5. they respond

解析：选D。根据未划线部分的提示，可以判断原句应该是由and连接的平行结构。根据平行结构中的成分必须在语法形式上一致的原则，可以明显看出theskills…, their ability… and how he or she responds…是不平行的，因为前两个成分是名词，而后一个成分是句子。所以只能选择D选项的名词theirresponses，这样才能跟前面的theskills和their ability构成平行结构。

小结

    考生一定要记背常见平行结构标志词。在考试中首先迅速敏锐地发现这些标志词，然后确认句子中的成分在语法形式上是否一致，这样就能快速准确地解题。

答案：1.C  2. D