为什么要用宾语从句，宾语从句出现的意义是什么，什么情况下用宾语从句，宾语从句的引导词改怎么选？

Question

如题所述

Answer 1

及物动词后和介词后接宾语，如果是从句就是宾语从句，引导词that无词意无成分，动词后面宾语从句that可以省略，whether/if有词意无成分。其它代词what which. who. whose，whom可以做主语，宾语，定语，表语，副词when. where. why.how等在从句中作状语或表语。如
I don't know if he can come.
I know that he can come.
I don't know why he came late.
I don't know where he went yesterday.
I don't know what he said.
I don't know how he came.