宾语从句中的that可以省略,定语从句中假如引导词that在从句中充当宾语,可以省略.
例如：宾语从句：I promise that I will study hard.这里的that可以省略
定语从句 This is the factory that we visited yesterday.这里的that可以省略
但是在这句中：This is the factory that lies in Guangzhou.这里的that做主语,不能省略.