2.表示转折关系的连词有：but, however, yet, still，while等。

Mary was a nice girl, but she had one shortcoming.

Tom got up early, yet he failed to catch the train.

He was very tired, still he kept on walking.

Your composition is fairly good, however, there is still some

room for improvement.

Jane is hard working ,while her sister is quite lazy.

3.表示选择关系的并列连词有：or, either…or…,whether… or…等。

1)or：或、否则

A:基本用法

or 表示 “或” 的意思，使用于两者之中选择一个的时候。

----Is your friend English or American? ----American.

He doesn’t like dumplings or noodles.

B:特别用法

祁使句后连接or ，表 “如果…,否则…”,有转折的意思，此时 or =if you don’t …,you’ll …

Hurry up, or you’ll be late.=If you don’t hurry up, you’ll be late.

2)either…or…:或者…或者…; 不是…就是…;要么…要么…

A. either…or…连接两个并列主语时,谓语动词靠近哪个主语就与哪个主语保持 “人称”和 “数”的一致，即就近原则。

Either you or I am right.

Does either she or they like English?

B. 由either…or…引导的否定句是完全否定。

She isn’t either a student or a teacher.

3)whether…or…不管…还是…

She is always cheerful, whether at home or at school.

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