a.连词：that, whether, if（这三个词都不作从句的成分，同时，that无含义，而whether和if都表“是否”）
b.疑问代词：who, whom, whose, what, which
c.疑问副词：when, where, why, how
①That the driver could not control his car was obvious.
②That she was chosen made us very happy.
③That he will come is certain.
④That he would take the risk is true.
⑤That he should have married her isn't surprising.
①It was obvious that the driver could not control his car.
②It made us very happy that she was chosen.
③It is certain that he will come.
④It is true that he would take the risk.
⑤It isn't surprising (that) he should have married her.
①Is it certain that he will come?
②Is it true that he would take the risk?
(1)it + be + 形容词+ that-从句
①It is likely that he will come.
②It is strange that she has ever trusted him.
③It is important that he（should) attend the meeting.
④It is best that he (should) go.
It is strange that no one should have objected to the plan.
(2)it + be +名词+ that-从句
It is common knowledge that the whale is not a fish...
It's a pity that he should have massed the train.
(3) it + be + -ed分词 + that从句
It is said that he is a famous writer.
It is reported that there will be a storm this afternoon.
It is suggested that the meeting(should）be held this afternoon.
It is demanded that he (should) leave at once.
(4) it + seem/happen/appear等不及物动词+that从句。（look不接that从句，它接to be结构或形容词）
It seems that he is wrong.
It appears that they are in urgent need of help.
He looks (to be) surprised/happy/sad.
Whether he will win the game is not clear.
Whether he will come is uncertain.
Whether she comes or not doesn't concern me.
It is not clear whether/if he will come.
It was uncertain whether he would come.