主語從句例子如下：
1、That he finished writing the composition in such a short time surprised us all.
他在如此短的時間內寫完作文使我們十分驚訝。
2、Whom we must study for is a question of great importance.
"我們為誰而學習"是個很重要的問題。
3、Whether we will go for an outing tomorrow remains unknown.
我們明天是否會去郊遊仍舊未知。
定義主語從句是在復合句中充當主語成分的句子。
壹、引導主語從句的連詞主要有:
1、從屬連詞:that、whether；
2、連接代詞:who、whoever、whom、whose、what、whatever、which、whichever、whomever；
3、連接副詞:when、where、how、why、whenever、wherever、however.
二、用it 作形式主語的結構：
1、It is +名詞+that從句
（1）It is a fact that ? 事實是?
（2）It is an honor that ?非常榮幸
（3）It is common knowledge that ?是常識
2、?it is +形容詞+that從句
（1）It is natural that? 很自然?
（2）It is strange that? 奇怪的是?
3、it +不及物動詞+that從句
（1）It seems that? 似乎?
（2）It happened that? 碰巧?
4、?it is+過去分詞+that從句
（1）It is reported that? 據報道?
（2）It has been proved that? 已證實?