在英语越来越普及的21世纪，英语水平的高低已经成了大学生是否能找到好工作的评定标准。为帮助大学生掌握权威的英语知识。特提供以下资料：
情态动词
情态动词表示说话的语气或情态。情态动词本身有词义，但不完全， 不能单独作谓语， 必须和动词一起构成谓语。
情态动词没有人称和数的变化。
大多数情态动词有过去式。
主要情态动词：
can, may, will ,must ,shall ,need, dare, had, better, would, sooner, would, as soon, could, might, would, have to, should, ought to, used to, would rather, might, as well
情态动词问题解析:
1. may be & maybe
May be (可能是)—maybe (或许)(副词)
The news may be true.
Maybe the news is true.
She may be waiting for you at home.
Maybe she is waiting for you at home.
2. May not & can not
may not 译为“可能不”、“也许不会”而非“不可以”。“不可以”为must not或can't(不许，不可以)。
---May I smoke here?
---No, you mustn't. /you can't /you can not.
The news may not be true.
You mustn't move any of the papers on the desk.
3. Can & be able to
Be able to 可以表示更多的时态。
We will be able to finish the work tomorrow.
He was not able to realize his greatest ambition.
Are you able to design a new computer program?
She has not been able to work out the complex problem.
4. ought to的否定式
ought to的否定式是ought not to，疑问句只把ought提前。
You ought to be responsible for yourself.
We ought not to look down on disabled people.
Ought we to count on him for the settlement of the debate?
5. Must
Must do
Must be
Must have done
6. Must 的反意疑问句
I must get up at six, ___?
She must be in the classroom now, _____?
They must have had great trouble trying to get there, ____?
7. 用must 提问时的回答
肯定回答：must
否定回答：needn't或don't /doesn't have to
Must I come as early as 6 tomorrow morning?
Yes, you must.
No, you needn't. / No, you don't have to.
8. Mustn't & Needn't
Must he arrive very early?
No, he doesn't have to / No, he needn't.
9. Must & have to
Must: 主观上认为“必须” 作某事。
Have to: 受客观情况迫使而“不得不” 作某事
You must work harder now if you want to find a satisfactory job after graduation.
Children in remote areas have to quit school simply because their parents cannot afford their education.
I must help him. {obligation, responsibility}
I have to help him. {unwillingness)
10. Must & have to的否定