早教吧 育儿知识 作业答案 考试题库 百科 知识分享

can,may,must,should不同点

题目详情
can,may,must,should不同点
▼优质解答
答案和解析
:①could也可表示请求,语气委婉,主要用于疑问句,不可用于肯定句,答语应用can(即could不能用于现在时态的简略答语中).如:
  Could I come to see you tomorrow?
  Yes,you can.(否定答语可用No,I'm afraid not.)
  ②can表示能力时,还可用be able to代替.如:
  I'll not be able to come this afternoon.
表示请求、允许时,might比may的语气更委婉一些,否定回答时(口语中常用) no ,you can't .or ,yes,please 用mustn't表示“不可以”、“禁止”、“阻止”之意(具有强烈禁止的意思)如:
  You may drive the car.
  — Might I use your pen?— No,you mustn't.
  用May I ...征询对方许可在文体上比较正式,在口气上比较客气.在日常口语中,用Can I ...征询对方意见在现代口语中更为常见.
  2.用于祈使句中表示祝愿.如:
  May you succeed!
  3.表示推测、可能(疑问句不能用于此意).
  He may be very busy now.
  4.“may(might) + have + 过去分词”表示对过去发生的行为的推测.如:
  He may not have finished the work.must和have to的用法  1.表示必须、必要.(must表示主观多一些而have to则表示客观多一些)如:
  You must come in time.
  回答must引出的问句时,如果是否定的回答,不能用mustn't,而要用needn't或don't have to.
  — Must we hand in our exercise books today?
  — Yes,you must.(No,you don’t have to.)
  2.“must be + 表语”的结构表示推测,它的否定或疑问式用can代替must.
  This must be your pen.
  3.“must + have + 过去分词”的结构常用在肯定句中,表示对过去发生的行为的推测.它的否定或疑问式用can代替must.
  He must have been to Shanghai.
  4.have to的含义与must相似,两者往往可以互换使用,但have to有各种形式,随have的变化而定.must与have to有下列几点不同:
  ① must表示的是说话人的主观看法,而have to则往往强调客观需要.如:
  The play is not interesting.I really must go now.
  I had to work when I was your age.
  ② must一般只表现在,have则有更多的时态形式.
  ③ 二者的否定意义不大相同.如:
  You mustn't go.你可不要去.
  You don't have to go.你不必去.
  ④ 询问对方的意愿时应用must.如:
  Must I clean all the room?
  注意:have to也可拼做have got to.