一、should与ought to用法辨析
1) should和ought to表示责任、建议或劝告，翻译为"应该"，后者语气强一些。
【例如】
You should listen to the doctor’s advice if you want to recover soon.
Such things ought not to be allowed.
2) should接动词的完成式，是一种谴责，表示过去应该做而没有做或过去做了而不应该做。
【例如】
I missed the class. I should have come earlier.
I shouldn’t have made such a foolish mistake.
二、need与have to 用法辨析
1) need表示需要，主要用于否定句和疑问句。用于疑问句，肯定回答用must，否定回答用needn’t。have to表示他人或客观情况要求"必须"，也可以翻译为"不得不"，have to否定形式意思是"不一定"或"没有必要"。
【例如】
You needn’t come if you don’t want to.
I don’t think you need be so polite to her.
You don’t have to work so hard if you just want to pass Band 4.
Because of the heavy rain, the children have had to get up earlier than usual this week.
It was very kind of you to do the washing-up, but you ____it.
A) mustn’t have done B) would not have done
C) might not have done D) didn’t have to
本句译为：你把这些东西洗了，你真是太好了。但是你没有必要洗。must, would, might后面接动词的完成式，都很少用否定式，而didn’t have to表示没有必要，符合题意，故答案为D.
2) need后面接动词的完成式，主要用于否定句，表示本可不必做某事。
【例如】
You ____ all those calculations! We have a computer to do that sort of thing.
A) needn’t have done B) must not have done
C) shouldn’t have done D) can not have done
"needn’t +不定式完成式"表示"本来不必做，但实际做了"。题意是：你没有必要做全部计算，这类计算我们用计算机来做。故答案为A.
三、used to的用法
"used to加不定式"表示过去常常干某事，现在不在干了。例如:
I used to go to work by bus. Now I take a taxi.
She used to be very shy.
"be used to doing"表示习惯于干某事。
【例如】
I am used to getting up early and going to bed early.
He is used to being praised by others.
四、情态动词must用法详解
1) must表示必须，否定回答时用needn’t. mustn’t表示不许可。
【例如】
You must get to the station before 3, otherwise you will miss the train.Must I hand in my homework tomorrow?
No, you needn’t. You can turn it in the day after tomorrow.
You mustn’t smoke in the hospital.
2) must用于肯定句，可以表示推测，翻译为：一定或想必。后面接动词的一般时，表示对现在的推测，接动词的完成式，表示对过去的推测。对过去的推测是考试的重点。
【例如】
She must live near here, for she comes to work on foot.
She was absent from class. There must have been something wrong with her.
The light was out. They must have gone to bed.
Mary’s score on the test is the highest in her class. She ____ have studied very hard.
A) may B) should C) must D) ought to
"must +不定式完成式"表示对过去发生事情的推测。题意为：玛丽的考试成绩全班第一，她学习一定很刻苦。答案为C.
五、情态动词shall的用法
shall用于第二、三人称，表示许诺、答应、命令等。
【例如】
If he passes the exam he shall have a holiday.
The law shall comes into effect on May 1st.
六、will与would用法辨析
1) will作情态动词，表示意愿、习惯等。would表示过去的习惯。
【例如】
It will be highly appreciated if you will send us your latest price list.
On Sundays he would get up early and go fishing.
2) Will/would you please do...,Would you like to do...,Would you mind doing...
都表示建议、询问、请求等。
【例如】
Will you please pass me a cup of tea?
Would you like me to give you a hand?
This box is too heavy, ____give me a hand?
A) would you mind B) would you please
C) will you like to D) will you please to
四个结构中，would you mind接动名词；would you please接动词原形；
will you like to不是正确结构；will you please to也不是正确结构，因此答案为B。 
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