定语从句中that可以省略吗？
如下：
一、定于从句：定语从句是指用一个完整的句子做定语去修饰限定前面的名词或者代词，它属于后置定语。
1、限制性定语从句不用逗号与主句隔开。
例：I have a sister who is a doctor.（限制性定语从句）我有一个当医生的姐姐。
2、非限制性定语从句需使用逗号和主句隔开。
例：I have a sister, who is a doctor.（非限制性定语从句）我有一个姐姐，她是当医生的。
二、定语从句的关系词。
引导定语从句的关系词分为：关系代词和关系副词。
常见的关系代词有：who, that,whom, whose, which等；在从句中作主语、宾语、定语等。
常见的关系副词有：where,when,why等；在从句中作状语。
三、定语从句中关系代词的用法。
1、当先行词是人时：关系代词who和that既可以做主语，又可以作宾语，而且作宾语时可以省略。
例如：Do you know the girl who/that often comes here?（作主语）
2、其中whom只作宾语。
例如：The girl who/that/whom I spoke to is my daughter.（作宾语）
3、当先行词是物时：关系代词which和that既可以做主语，又可以作宾语，而且作宾语时可以省略。
例如：The building which/that stands near the train station is a supermarket.（作主语）
4、whose既可以指人，也可以指物；that既可以指人，也可以指物。
例如：The book which/that you bought for me is very interesting.（作宾语）
5、whose既可以指人，也可以指物；在从句中作定语，形式为“whose+名词”表所属关系，即谁的。
例如：Do you know the singer whose name is Wang feng?
I live in a house whose windows face south.
四、定于从句中只用which不用that的情况：
（1）which引导非限制性定语从句，that则不能。
He had failed in the maths exam,which made his father very angry.
（2）在介词提前的定语从句中，只用which不用that。
This is the place in which Lu Xun used to live.
先行词本身是that时，只能用which。
What’s that which flashed in the sky just now?
五、关系副词引导的定语从句。
1、when指时间在定语从句中作时间状语也可做连接词用。
I still remember the day when I first came to the school.
2、where指地点在定语从句中作地点状语。
Shanghai is the city where I was born.
3、why指原因在定语从句中作原因状语，用在reason后面。
Please tell me the reason why you missed the plane.
