连接代词和连接副词在句中既保留自己的疑问含义又起连接作用，在从句中充当成分。

　　That she was chosen made us very happy.

　　她被选上了使我们很高兴。

　　Whether they would support us was a problem.

　　他们是否会支持我们还是一个问题。

　　When the plane is to take off has not been announced.

　　飞机何时起飞还没有宣布。

　　[名师点津]　if不能引导主语从句。

　　3．用it作形式主语的主语从句

　　主语从句可以直接放在句首，有时为了平衡句子结构或表示强调，常用it作形式主语，而将作真正主语的从句放在后面。

　　常以it作形式主语的句型有：

　　It's certain that she will do well in her exam.

　　毫无疑问她的考试成绩会很好。

　　It's a pity that we can't go.

　　很遗憾我们不能去。

　　It's said that Mr.Green has arrived in Beijing.

　　据说格林先生已经到了北京。

　　It happened that I was out that day.

　　碰巧我那天外出了。

　　It is clear what he meant.

　　他是什么意思很清楚。

　　[即时演练2]

　　(1)单句改错

　　①Bob failed in the exam disappointed his parents.Bob前加That

　　②If Peter will attend the ceremony remains unknown.If→Whether

　　③That Alice said at the meeting was of great value.That→What

　　(2)完成句子

　　①很遗憾他没来。

　　It's_a_pity_that he didn't come.

　　②他们是否会支持我们还是一个问题。

　　It_is_a_problem_whether they will support us.

(二)宾语从句