① that 在引导的同位语从句中只起引导词的作用,在从句中不充当任何成分,但不可以省略。
He came to the decision that he must act at once .
② whether 引导同位语从句时,在从句中不作成分,意为"是否"不能省略,不能用 if 替换。
He asked her a question whether they can be friends .
③特殊疑问词 how , where , when , why 等引导同位语从句时,在从句中充当句子成分。
I have no idea why he brought that up again .
拓展