20. 连词
连词不能独立担任句子成分而只起连接词与词，短语与短语以及句与句的作用。连词主要可分为两类：并列连词和从属连词。并列连词用来连接平行的词、词组和分句。如：and, but, or, nor, so, therefore, yet, however, for, hence, as well as, both…and, not only…but also, either…or, neither…nor, （and）then等等。
20.1 并列连词与并列结构
并列连词引导两个并列的词、词组或句子。
1） and 与or
判断改错：（错）They sat down and talk about something.
（错）They started to dance and sang.
（错）I saw two men sitting behind and whisper there.
（对）They sat down and talked about something.
（对）They started to dance and sing.
（对）I saw two men sitting behind and whispering there.
