针对学生们常见的一些练习和考题，我们总结了一下几种特殊替代用法： it 在句中作形式主语或形式宾语的替代用法
1. it作形式主语可以代替句中的动词不定式、动词-ing分词或一个句子。 It is important for us to learn English well. (it替代不定式to learn English)
It is no use making such an apology to us Chinese. ( It 替代动词-ing分词 making such an apology)
It is happy for her parents that she is well now. (it 替代句子that she is well now)
2. it作形式宾语可以代替句中的动词不定式，此时句中的谓语事由某些特殊动词 (如：find think feel等)充当的。
I find it impossible to finish so much work in such a short time. (it 替代不定式to finish so much work)
A: I’m going to wear my new jeans to her party.
B: You can’t do that. (that替代to wear my new jeans to her party这一事情)
A: Hi, Mr. Smith, This is my friend, Bill.
B: Nice to meet you, Bill.
C: Nice to meet you, Mr. Smith.
A: Hello, may I speak to Miss Li?
B: This is Miss Li speaking. (我就是李女士)
1. which 在句中放指物的先行词后或整个句子后，引导限定性定语从句或非限定性定语从句。
She said I was lazy, which isn’t true.( which替代句子 She said I was lazy)
This is the pen which was bought by my father. (which替代的是 the pen)
2. that在句中放先行词后，引导限定性定语从句。既可指物，也可指人。 The book that she borrowed from the library was lost. ( that替代的是The book) The man that with a knife in his hand is a murderer. (that替代的是The man )
3. who、whom(whom在定语从句中作宾语)在句中放指人的先行词后，引导限定性定语从句。 She was the girl who whom I just talked to. ( who whom替代的是 the girl 且作to 的宾语)
one 为避免重复而替代前文所提及的可数名词的单数，且该中心名词可以用one 或a、an修饰表示“一”;若替代前文提及的可数名词复数，则用ones.
There are many books on the shelf, which one do you like best? (此处的one 替代的是book) There are many pens in my hand, and the blue ones are mine. (此处的ones 替代的是 pens) 量词的替代用法
当前文有某些可数名词复数(如pants、jeans、shorts、glasses等)时，如果这些名词前面没有a pair of 或 a suit of修饰时，则不能用one 来替代上述这些词，因为这些词前面不能用基数词直接修饰(我们不能说2 pants或5 clothes或 one shorts), 而是用可以修饰它们的量词短语中的量词来替代。
The pants are too small for me, Can you show me another pair? (因为another后面只能跟单数可数名词，故而这里用pair代替，意为a pair of pants)
The red pants are too small for me. Can you show me the blue ones. (此处ones替代的是pants)
The paper is too small for the little girl to paint on, please give her another piece.(因为有a piece of paper)
I’m so hungry that this slice of chicken isn’t enough. Could you give me 3 more slices?(代替的是3 more slices of chicken.)
1) A: Look! There are many bottles of milk on the desk.
B: Yes, and which one do you like best? (此处用one的原因是A句中已经出现bottles of milk, 所以可以代替one bottle of milk)
2) A: There is much milk on the desk.
B: Yes, but which bottle bag do you like best? (此处A句中心词为milk,因为milk 前面不能用one 来直接修饰，而只能用bottle或bag 来代表数量，可以说a bottle of milk a bag of milk)
1) A: Where is Jeanie?
B: Oh, she is at Mary’s. (这里的Mary’s代替的是Mary’s house)
2) Yesterday Tom’s father was ill, now he is at the doctor’s. ( 这里的doctor’s代替的是doctor’s room 或doctor’s clinic)