Whether he ll be able to come is not yet known.
Why they have not left yet is unclear.
我们可以用it来做形式主语。
如：It was good news that everyone got back safely.
我们可以用名词性从句来做动词的宾语。
如：she sensed that she was being watched.
I wonder if/whether that s a good idea.
Polly didn t know which way she should go.
我们可以用名词性从句来做介词的宾语。
如：I m interested in who that tall man is.
There was a discussion about whether Polly had found the blind man.
我们可以用it来做形式宾语。
如：we all thought it good news that the fog had finally gone.
The conductor has made it clear that no buses will be running.
我们可以用名词性从句来做表语。
如：the truth is that the fog is too think for the bus to run that far.
My question is whether Polly can find her way home.
The problem is how Polly is going to find us in the crowd.
我们可以用名词性从句来做一个名词的同位语。
如：the fact that Polly didn t ask for the man s name is a pity.
The news that the plane had crashed made us sad.
Whatever gave you the idea that I can sing?
我们用that，if/whether或一个疑问词来引导名词性从句。
如：I hope that Polly will be OK.
No one knew if/whether he lost his sight because of an accident.
She couldn t imagine how the blind man had found her.
二 名词性从句：用that或if/whether引导的名词性从句
1．我们用that 来引导名词性从句。
1）当从句是一个陈述句时，我们用that来引导名词性从句。
如：She sensed that she was being watched by a tall man in a dark coat.
2) 在大多数情况下，我们不用that来引导介词后的名词性从句，但是，可以用that来引导in或except后的宾语从句。
如：The problem lies in that the mist may become a thick fog.
I didn t tell him anything except that I wasn t able to find my way back.
3）当名词性从句做句子的主语时，that不能省略。
如：That we couldn t find our way out was really bad news.
4）在非正式英语中，当名词性从句做句子的宾语或表语时，that可以省略。
如：She wished (that) someone would come along to help her.
The truth is (that) the buses will not be running.
我们用if或whether 来引导名词性从句。
当从句是个一般疑问句时，我们用if或whether来引导名词性从句。我们把if或whether后面从句的顺序改成陈述句的语序。
如：She wondered. Would the buses still be running?
