介绍:
主语从句：
This is really good news. 单词作主语
Plenty of food is really good news. 短语作主语
That her house survived the earthquake is really good news. 句子作主语
表语从句：
表语从句放在连系动词（be、seem、look、appearence等）之后，充当复合句中的表语。
The question is important. 单词作表语
The question is from the sales department. 短语作表语
The question is which work should he be done first. 句子作表语
宾语从句：
Bobody knows it. 单词作宾语
Nobody knows the exact date. 短语作宾语
Bobody knows when he can arrive.句子作宾语
要有整体观来判别句子成分！
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