What you need is more practice.
Whatever was said has left us much to think.
Whoever wants it may have it.
what, who, whom, whose, which, whatever, whoever, whichever
It was strange that he had made a mistake.
That we need more equipment is quite obvious.
Whether he will join us won't make too much difference.
(It's won't take too much difference whether he will join us.)
It's clear (that) he has done his best.
It's a wonder (that) he didn't fail.
When they will come hasn't been made public.
Where she has gone is not known yet.
How the prisoner escaped is a mystery.
(It's mystery how the prisoner escaped.)
Why he did it will remain a puzzle for ever.
when, where, how, why
What the police want to know is when you entered the room.
The trouble is that we are short of funds.
This is what we should do.
That's why I want you to work there.
His first question was whether Mr. Smith had arrived yet.
as if, as though, because也可用來引導名詞子句。
She seems as if she had done a great thing.
It is because you eat too much.