请帮我讲解一下英语中主语从句和让步状语从句

请帮我讲解一下英语中主语从句和让步状语从句

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主语从句
1．主语从句主要有三类：
（1）由连词that引导的主语从句.
例如：That you will win the medal seems unlikely.
你想获得奖牌看起来是不可能的.
That you are so indifferent bothers me.
你如此冷淡使我很烦恼.
That she survived the accident is a miracle.
她在事故中幸免于难简直是奇迹.
（2）用连接代词或连接副词Which When Whethe引导的主语从句.
例如：Which of them escaped from the prison is stilla mystery.
他们哪一个是从监狱里逃跑的,仍然是个谜.
When they will come hasn’t been made pubic.
他们什么时候来还不知道.
Whether she is coming or not doesn’t matter toomuch.
她来不来都无关紧要.
（3）用关系代词引导的主语从句.
例如：What you need is more practice.
你所需要的是更多的训练.
What I want to know is this.我想知道的就是这事.
Whatever we do is to serve the people.
我们无论做什么都是为人民服务.
主语从句可以直接放在主语位置上,也可以用it作形式主语,
而将从句放在句末（尤其是当谓语较短时）.
例如：That light travels in straight lines is known toall.
光沿直线传播,这是众所周知的事.
=It is known to all that light travels instraight lines.
众所周知光沿直线传播.
When the plane is to take off has not beenannounced .
飞机何时起飞还没有宣布.
= It has not been announced when the plane is totake off.
还没有宣布飞机何时起飞.
当what引导的主语从句表示“…的东西”时,一般不用it作形式主语.
错:It is a book what he wants.
对:What he wants is a book.他想要的是本书.
如果带主语从句的句子是疑问式,则必须用it作形式主语的结构.
例如：Has it been settled who will be sent to carryout the task
谁将被派去执行这项任务决定了吗?
让步状语从句
表“虽然”、“尽管”、“即使”等概念的从句,叫让步状语从句.
让步状语从句通常由下列连词引导：although(though)（虽然）,as（尽管,虽然）,even if(though)（即使）,however（尽管）,whatever（不管）；nomatter (how,what,where,when)（不管（怎样、什么、哪里、何时））,whether…or（不管）.although和though在意义上没有区别,但although语气上要强一些,所以更常用于句首.例如：
Although he ispoor,he is honest.
他虽然穷,但是诚实.