在通常情况下,我们会用形式主语it代替主语从句放在句首,而将主语从句放在句末,以避免句子头重脚轻。如: That we shall be late is certain. 我们要晚了,这是确定无疑的。http://yingyu.chazidian.com =It is certain that we shall be late. 我们肯定要迟到了。 What she did is not yet known. 她干了什么尚不清楚。 =It’s not yet known what she did. 她做什么还不得而知。 但是,如果如是感叹句,则必须用形式主语it。如: How strange it is that the children are so quiet! 真奇怪,孩子们如此安静!