1、That he finished writing the composition in such a short time surprised us all.
他在如此短的时间内写完作文使我们十分惊讶。
2、Whether we will go for an outing tomorrow remains unknown.
我们明天是否会去郊游仍旧未知。
3、Who will be our monitor hasn't been decided yet.
现在还没有决定谁会成为我们的班长。
4、Whom we must study for is a question of great importance.
“我们为谁而学习”是个很重要的问题。
5、What caused the accident remains unknown.
事故的起因是未知的。
扩展资料：
用it 作形式主语的结构
(1) It is +名词+that从句
It is a fact that … 事实是……
It is an honor that …非常荣幸
It is common knowledge that …是常识
(2) it is +形容词+that从句
It is natural that… 很自然……
It is strange that… 奇怪的是……
(3) it +不及物动词+that从句
It seems that… 似乎……
It happened that… 碰巧……
(4) it is+过去分词+that从句
It is reported that… 据报道……
It has been proved that… 已证实……
参考资料来源：百度百科-主语从句
