为什么要用 that 能不能不用that

此处是用that引导的定语从句，只有当引导词that做定语从句的宾语成分时可以省略，其他情况不能省略。此句中that是做从句的主语 所以不可省略。

看下面例子：

The man [(that) I saw in the street yesterday] is my teacher.

The man [that said hello to me yesterday] is my teacher.

The village [(that) I often visit] is my hometown.

The village [that becomes a modern city] is my hometown.

注：带（）的that可以省略，[ ]括着的是定语从句。