do so, do that(it)
do so和do that(it)常用来代替前面的动词短语，以免重复。一般说来，当被代替的动词是表示动作的动词和短暂动词时，do so, do that(it)都可以使用，并无多少差别。如：
John drank too much yesterday.I wonder why he did so/that/it.但是，在较规范的英语中，do so和do that在以下场合不能混用。
1.do so主要用来表示同一主语所做前面刚提到过的同一动作。如：I promised to get the tickets, and I will do so as soon as possible.The doctor said,“Now, breathe deeply, Charlie.”Charlie does so.
注意：如果动作的发出者是前面句子的宾语，也多用do so.如：A man asked the writer to look after his parrot and the writer said he would do so.
2.当do本身以不定式、现在分词和动名词等形式出现时，不管被替代的是谓语动词还是非谓语动词，其后一律接so。如：
They didn’t work yesterday and instead of doing so, they went to the cinema.We decided not to go.To do so would have made things very difficult.
3.当替代动词do的主语与前面所提到的句子的主语不同时，应该用do that或do it.
如：Tom suggested emptying all the pockets on the table, but the owner of the pub would not let them do that.
I haven’t got time to get the tickets.Who’s going to do that?
4.注意，在某些特定的场合，do so, do that,甚至do it, 表示的意义也是不一样的。试比较：
Bob’s getting his house painted, and moreover, he wants me to do so.(He wants me to get my
house painted.)
—Bob’s getting his house painted!
—And I’d like to do that, too.(I want to get my house painted, too.)
Bob’s getting his house painted, and morevoer, he wants me to do it.(He wants me to paint his house.)
