主语从句就是一个从句,它做另一个句子的主语.
主语从句在复合句中作句子的主语.引导主语从句的词有连词that,whether; 连接代词who,what,which; 连接副词when,where,how,why等.如：
What is needed for the space trip is careful preparation.
Whether wild life can be well protected is of great importance.
Who will go makes no difference.
Why dinosaurs died out remains a puzzle.
Which kind of food is the best is still not certain.
为了避免主语显得过长,可以用it作为句子的主语,把主语从句移到句子的末尾.如：
It hasn’t been decided yet when the new restaurant will open.
It is not clear how gold was found there.
It is hard to understand why there is gravity.
It is a shame that you have to leave so soon.
宾语从句（The Object Clause）
宾语从句在复合句中作主句的宾语.宾语从句通常由下面一些词引导.
（1）x05由that引导（that在口语或非正式文体中常省略）.如：
I don’t think (that) differences are important in a friendship.
Some readers said (that) they are going to eat more vegetables.
An old lady said (that) she found a job as a foreign language teacher.
I think (that) women can reach very high achievements in many fields of science.
(2)由连接代词或连接副词引导.如：
Thomas wants to know where Nina lives.
He wants to know what she thinks of the transportation.
It is interesting to hear what the class think about action movies.
I dinn’t know who the man was.
Do you know who (whom) John Adams was speaking to?
He asked whose spacesuit it was.
Pay attention what the doctor said,will you?
He can’t tell which gesture means “good luck”.
Please tell me when JoeWilliams won the Nobel Peace Prize.
I don’t know where Charlie Chaplin got his stick.
Will you tell me how I can keep fit and healthy?
Do you know why he crossed his arms?
(3) 由连词whether或if引导（口语中常用if）.如：
She asked me if she could borrow these books.
I wonder whether (if) Lin Qiaozhi remembered how many babies she had delivered.