that 引导的主语从句中that可省吗?

问题描述:

that 引导的主语从句中that可省吗?

1)that引导宾语从句,在句中不做成分,用作连词,通常可略
I think that he is very clever.
2) 引导主语从句,在句中不做成分,用作连词,通常不略
3) 引导同位语,表语从句,不做成分,不能略
4) 引导定于从句,必做成分,做主语时不能略,宾语可以略