主语从句
句型：
It is +名词+从句
It is a fact that… 事实是……
It is good news that … ……是好消息
It is a question that … ……是个问题
It is common knowledge that … ……是常识
类似的名词还有：a pity；a wonder；a good thing； no wonder； surprise等.
例如：It is a mystery to me how it all happened.
这一切是怎么发生的是个谜.
It is common knowledge that the whale is not a fish.
鲸鱼不是鱼,这是常识.
It is no surprise that Bob should have won the game.
鲍勃会赢得这场比赛,这不足为奇.