请看：
1.She asked him to leave, (and) so did I.（代词）
2. She asked him to leave, (and) so he did.（连词）
3. She asked him to leave.
So she did.（代词）
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译文如下：
1. 那时她要求过他离开，而且我也要求他离开。
2. 那时她要求过他离开，所以他离开了。
3. 那时她要求过他离开。
是的，她的确要求过。
1.主句的一种肯定的表述，其从句中主语（即第二个主语）也完全做了同样的事情或情况完全相同时，这个从句要用代词so引导，并采取部分倒装，并使用简略形式，须根据主句来判断从句中助动词的使用。若前句谓语是实意动词，则倒装结构中用助动词do的正确形式；若前句谓语动词含有be动词或have等助动词，则倒装结构中用be动词或助动词的正确形式；若前句用情态动词，则倒装结构中用情态动词的正确形式。如上述例句1，再如:
I like swimming, so does she.
我喜欢游泳。她也喜欢。
She succeeded，so did I。她成功了，我也成功了。
She is a good student，so am I.
她是一个好学生，我也是。
She has been there. So has her brother.
她去过那儿。她兄弟也去过那儿。
She will go to the park，so shall/will I.她将去公园，我也是。
如主句时否定句，则so要换成neither/nor,同样实行部分倒装：
I don’t like swimming, neither/nor does she.
我喜欢游泳。她也喜欢。
She succeeded，neither/nor did I。她成功了，我也成功了。
She is not a good student，neither/nor am I.
她不是一个好学生，我也不是。
She has not been there. Neither/Nor has her brother.
她没去过那儿。她兄弟也没去过那儿。
2. 主句的一种表述，从句对主句描述的情况加以支持或确认、强调等时（要点是从句的主语和主句的主语相同），这个从句不必采取部分倒装形式，并使用简略形式，须根据主句来判断从句中助动词等的使用。如例3。再如：
She asked him to leave.
So she did.
那时她要求过他离开。
是的，她的确要求过。
The keys are in the ignition.
So they are.
汽车钥匙插在点火器里。
是的，钥匙插在点火器里。
3. so用作连词，主要用于表结果，意为“所以”,从句不必倒装，如上述例句2的用法，再如：
The door was locked, so we couldn’t get in.
门上锁了，所以我们进不去。
I couldn’t have won, so I didn’t go in for the race.
我不可能获胜，因此我没参赛。
The play began at eight, so they must dine at seven.
戏八点开始，因此他们必须七点吃饭。
It was dark, so I couldn’t see what was happening.
天很黑，所以我看不见发生了什么事。
There happened to be a policeman on the corner, so I asked him the way. 恰好拐角处有一位警察，我就向他问路了。
He told me to do it and so I did it.
他叫我那么做，所以我就做了。
He worked hard and so he succeeded.
他勤奋工作，所以他取得了成功。
There was so much to eat and so few people to eat it.
有这么多东西可吃，而吃的人又这么少。
I forgot to post the letter, and so she never heard about my divorce.
我忘了寄那封信了，所以她一直不知道我离婚的事。
4.so作副词或形容词：
The ticket was so expensive that we couldn't attend the show.
So expensive was the ticket that we couldn't attend the show.
门票太贵了，我们看不了这演出。（部分倒装）
I ran so quickly that I won the race.
So quickly did I run that won the race.
我跑得非常快，结果赢得了比赛。（部分倒装）
The movie was so boring that I fell asleep.
So boring was the movie I fell asleep.
这部电影太无聊了，以至于我睡着了。（部分倒装）