系动词
系动词，亦称连系动词（Link Verb）。作为系动词，它本身有词义，但不能单独用作谓语，后边必须跟表语，亦称补语（形容词），构成系表结构说明主语的状况、性质、特征等情况。英语除动词be 之外，还有一些动词也可以做系动词，如表示状态或情况的：keep, look, feel, appear, lie, remain, seem, stay, smell, sound, taste等；以及表示变化的：get, grow, turn, fall, run, become, go, 等。
1. to be 可以加在seem, prove, remain, appear 等系动词和其后的名词或形容词之间，但也可以省略。
E.g. The task proved (to be) impossible.
E.g. They seem (to be) such friendly people, but they never replied to our invitation.
注意：在seem, appear 等词后，可加其他非to be 不定式，但这时他们不是系动词，而是不及物动词。
Courtesy, politeness, good manner? Call it what you will, the supply never seems to equal the demand.
非人称代词it
做句子的形式主语
1. 代表不定式
E.g. It is absurd to be afraid under such circumstances.
2. 代表动名词
E.g. It is terrible trying to keep up with the Jones.
3. 代表that 引导的从句
E.g. It is plain to everyone that she was offended.
4. 代表wh- 引导的从句
E.g. As long as he finishes his work, it doesn’t matter when he comes to the office.
做句子的形式宾语
1. 代表不定式
E.g. They found it difficult to get along with him.
2. 代表从句
E.g. I think it best that you (should) stay with me.
E.g. He soon made it clear why he had asked a conference.
用来改变句子结构，使句子某一成分得到强调
1. 强调主语
E.g. It was she who put forward the suggestion.
2. 强调宾语
E.g. it is that painting that he has sold at a good profit.
3. 强调状语
E.g. it was through me that he has got the present job.
强调
用so 表示强调
用so 强调听者同意说者所言，这种用法只将so 提到句首，其他成分位置不变。
E.g. –you have spilled coffee on your dress.
- So I have.
情态动词+完成式
could+have+过去分词
有时表示过去的时间，说明某事可能已发生，有时也表示与事实相反，表示本来有能力做某事，但却未做。
E.g. What happened in the airport could have been true.
might/may+have+过去分词
表示对已经发生的情况进行揣测，但语气相当不肯定，表示近乎未实现的行为.
E.g. You might have done the work better.
must+have+过去分词
是对发生在过去的一种行为的推测，表示过去必定发生过的事情，语气相
当肯定，表示“肯定，一定”。
E.g. It must have rained last night. The ground is wet.
should/ought to +have+过去分词
表示该做而未做到的事，表示“本应”。
E.g. They should have made a good job of it.
should not/oughtn’t to+have+过去分词
表示做了不该做的事，表示“本不应该”。
E.g. You should not have done such things.
can’t（couldn’t）+have+过去分词
表示对过去的动作进行否定性推测。意为“肯定没有，肯定不是”。
E.g. The poem can’t have been written by the little girl; she is only four.
would+have+过去分词
经常用于虚拟条件句中，表示与过去事实相反的猜测。
E.g. If she had known about it, she would have talked about it.
needn’t+have + 过去分词
表示不必做的事情却做了，可译为“原本不必”“其实不必”。
E.g. You ne edn’t have done all these calculations. We have a computer to deal with that sort of thing.
主谓一致
知识点一many a, more than one +单数名词，谓语仍然用单数。
E.g. Many a soldier has sacrificed his life for the revolution.
知识点二either of +复数名词，谓语动词用单数．
E.g. Has either of your parents visited you?
知识点三and; both and
连接两个单数形式的名词词组，谓语动词用复数．当主语在意义上指同一人，同一物或同一概念时，谓语用单数．
E.g. A boy and a girl want to go.
知识点四each and each; every and every 等结构后，谓语用单数．
E.g. Each man and (each) woman is asked to help.
知识点五主语后面有as well as; together with; along with; rather than等词组，谓语的单复数有主语来决定．
E.g. I, together with my mother, was reading at ten yesterday.
one of＋复数名词＋关系分句结构
如先行词为复数名词，谓语则为复数．当前面有the only/very等限定词修饰，谓语用单数．
E.g. Joan is one of those people who go out of their way to be helpful.
靠近原则：
由not only...but also, either...or, neither...nor 或or 连接的并列主语。通常根据就近一致原则，谓语动词的单复数形式由最接近它的名词词组的单复
数形式决定。
E.g. He or you have taken my pen.
由“a number of, a total of + 复数名词”作主语谓语动词用复数形式；
由“the number of, the total of+ 复数名词”，谓语动词用单数形式。
E.g. A number of students are waiting for the bus.
倒装句
