一、should與ought to用法辨析
1) should和ought to表示責任、建議或勸告，翻譯為"應該"，後者語氣強一些。
【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接動詞的完成式，是一種譴責，表示過去應該做而沒有做或過去做了而不應該做。
【例如】
i missed the class. i should have come earlier.
i shouldn’t have made such a foolish mistake.
二、need與have to 用法辨析
1) need表示需要，主要用於否定句和疑問句。用於疑問句，肯定回答用must，否定回答用needn’t。have to表示他人或客觀情況要求"必須"，也可以翻譯為"不得不"，have to否定形式意思是"不一定"或"沒有必要"。
【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
本句譯為：你把這些東西洗了，你真是太好了。但是你沒有必要洗。must, would, might後面接動詞的完成式，都很少用否定式，而didn’t have to表示沒有必要，符合題意，故答案為d.
2) need後面接動詞的完成式，主要用於否定句，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"本來不必做，但實際做了"。題意是：你沒有必要做全部計算，這類計算我們用計算機來做。故答案為a.
三、used to的用法
"used to加不定式"表示過去常常乾某事，現在不在幹了。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"表示習慣於乾某事。
【例如】
i am used to getting up early and going to bed early.
he is used to being praised by others.
四、情態動詞must用法詳解
1) must表示必須，否定回答時用needn’t. mustn’t表示不許可。
【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用於肯定句，可以表示推測，翻譯為：一定或想必。後面接動詞的一般時，表示對現在的推測，接動詞的完成式，表示對過去的推測。對過去的推測是考試的重點。
【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"表示對過去發生事情的推測。題意為：瑪麗的考試成績全班第一，她學習一定很刻苦。答案為c.
五、情態動詞shall的用法
shall用於第二、三人稱，表示許諾、答應、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與would用法辨析
1) will作情態動詞，表示意願、習慣等。would表示過去的習慣。
【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...
都表示建議、詢問、請求等。
【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
四個結構中，would you mind接動名詞；would you please接動詞原形；
will you like to不是正確結構；will you please to也不是正確結構，因此答案為b