问题一：
一can 1.表"能力"I can lift the stone. I can speak English while he can't. Who can play the violin? He got up early yesterday so that he could catch the early bus.
could 表过去的能力。
注；1。can 与be able to表能力时的区别：
① 形式上；can有两种形式can 与could，而be able to有更多的形式。
is(are)able to, was able to ,, has been able , will be able to , would be able to 等。
be able to 只表能力而can 还可表"可能性"，"惊异","许可"等。
② could与was able to表过去能力的差别：均表过去的能力，但was（were）able to还可表业已成功的行为（即：动作确实做了）。
2．表"许可"You can go now. You can use my dictionary. You can have a rest.
-Can I smoke here?
-No, you can't.
注：用could代替can在疑问句中，语气客气委婉，但在时间上还指现在.Could you lend me your bike? Could you tell me how to get to the station?
注意：回答由could引起的问句，仍用can 而不用could。
-Could you wait a few more minutes?
-Yes, I can.
3.表猜测"可能"，一般用于疑问句和否定句。
-Can the news be true? -It can't be true. Where can he be?
注：(1)can't表"不可能"，语气断然否定。
(2) could在宾语从句中表过去的可能性，其它情况一般还表示现在的可能性只是语气比can委婉和更加不肯定。 I thought he could come .
(3) can 亦可用于肯定句表可能，但表示的是逻辑推理上的可能性（或理论上的），非主观臆断。There can be no noise on the moon because of sound being carried by the air .
(4) can(could)…have done或can(could)…have been(done)用于疑问句或疑问句表对过去时或完成时的揣测。
What can have happened to him ? He can not have read the book. He can't have been to Beijing.
4.表"惊异""惊讶"：How can you be so impolite? How can you say that?
问题二：
. Will 1。表"意志，意愿，乐意"，用于各人称 。（与will作助动词表时态区分开来）。
I will tell you all about it.相当于I am glad to tell you all about it.
He won't go there.他不愿意去那里。
2． Will在疑问句用于第二人称，表示询问对方的意愿或向对方提出请求。
Will you go with me for a walk? Do come to my birthday party , will you?
Will you please tell me how I can get to the station ? Won't you sit down?
3. 表示习惯性动作，有；"总是，总要，"，"惯于"的意思 。
Fish will die out of water。鱼离开水总是要死的。
He will talk for hours if you give him the chance .你要给他机会的话他总是要谈上几个钟头 。
.Would (是will的变形，与will的用法相对应。应把would作助动词表时态区分开)。
1． 表"意愿"用于人称。 He said he would help us.他说他乐意帮助我们。
2． 表说话人的意愿或向对方提出请求，语气比will更客气婉转，但指的是现在时间。
Would you like some bananas ? I'd rather stay at home than go out .
Would you mind opening the window for me ?
注意：用would提出的一般疑问句，回答时要还原为will。-Would you help me with my lessons? -Yes, I will.
3. 表过去的习惯动作。
She would drop in on her teacher when she went to town .她总是要顺便看一下老师。
Every day she would get up early at six o'clock.过去她总是每天6点起床。
She would sit like that for hours watching ships.她过去总是坐在那里几个钟头看船。
3． 用于虚拟语气或用于科幻作品中。Such would be our home in the future.
我们未来的家庭就是这样。
简言之：could和would具有表“虚拟语气”的功能，听起来更委婉，也更符合英国人的用语习惯。
希望对你有所帮助
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