that 常用作指示代词，不管作哪种句子成份，一般不省略，但在下列情况下有时可以省略：
1．用作代词，代替前面所指的事物，常见于表示比较关系的状语从句中，例如：
   It is warmer in the south than ( that of )the south。
  
2．引导名词性从句作宾语，即宾语从句，例如：
   She said ( that ) she would come。
   I suggested ( that )we ( should ) go home。
3．作关系代词，在定语从句中作表语或宾语，例如：
   Can I have the records ( that ) I lent you?
   He is just the man ( that ) you talked about。
   
4．在 way （意为 manner ）后面，that 意思为 in which，例如：
   Do it the way ( that ) I showed you。
5．在表示个人对事物反应、表示重要性或迫切性的adj后所接的从句中，例如：
   I am glad ( that ) you are right。
  
   It is obvious ( that ) they are happy together。
6．so that, so…that, such…that, 结构中，例如：
   I came to see you so ( that ) you would know the truth。
  
   She had so many children ( that ) she didn’t know what to do。
   I was having such a nice time ( that ) I didn’t to leave。
  
7．用于表示时间的词后面，整个短语相当于when，例如：
   I joined the army the year/month ( that ) my father died。
   Mac came to see me the week ( that ) we went camping。
  
   The time ( that ) you knocked at the door, my telephone rang。
   I thought her nice and honest the first time ( that ) I met her。
  
   = I though her nice and honest when I met her。
8．如果定语从句中的谓语是 there is，作主语的关系代词 that 也常省略，例如：
   This is the fastest train ( that ) there is to Beijing。
  
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