that 引导的是定语从句,且在从句中充当主语!所以不能省略,省略了从句就不完整啦!
另外省略常常用于以下情况：
1、关系代词which,whom,who,that在定语从句中作宾语时可以省略.
Here is the man (who/that/whom)you're been looking for.
2、当that在从句中作补语时可以省略.
He is not the man (that) he used to be.
3、当先行词是reason,而且定语从句中作原因状语时,关系代词可用why,that,也可以省略.
The reason (why/that) he failed was his laziness.
That is the reason (why) I did it.
5、当先行词是way,且在定语从句中作方式状语时,关系代词可用in which,that,也可以省略.
The way (in which/that) these comrades look at problems is wrong