Question

I know the girl. She is reading under the tree. (合并为一句) I know the girl under the tree。

Answer 1

• I know the girl who is reading under the tree.

• 用来引导定语从句。它代表先行词，同时在从句中作一定的句子成分。
  关系代词有主格，宾格和属格之分，并有指人与指物之分，它在先行词和定语之间起纽带作用。
  主要的关系代词有who,whom,whose,which和that。 
  ①who指人，在定语从句中作主语或宾语；
  whom指人，在定语从句中作宾语；
  whose在定语 从句中作定语，其先行词既可以是人也可以是物。 
  例如：The teacher who/whom you want to see has come. 
  ②which指物，在定语从句中作主语或宾语。 
  例如：Here is the coat which will be made to you. 
  ③that多指物，有时也指人，在定语从句中作主语或宾语。 
  例如：I have eaten bread that/which he gave to me.