手机短信验证
1. could/can和“能力”，即：ability
表示“能力（have the ability）”两者区别仅在于时态。
The machine can translate simple messages into 24 different languages.
They couldn’t afford to pay fora proper funeral.
I couldn't read then but now I can.
语法易错题
英语单词快速记忆
初中英语试题
2. could/can和“推测可能性”，即：possibility
表示推测“有可能”，can仅仅用于否定和疑问句，肯定句中则对应为must。
如果按照推测的把握性，从弱到强排序如下：
might¬——may——could——should——must/can——will
可见：could是“中度”，而can't则表示“（绝无）可能”。
How can I work with all this noise going on?
How can I possibly refuse such a charming invitation?
Can there be any doubt about his intentions?
Surely he can’t have forgotten about the wedding!
We could still win –the game isn’t over yet.
Ina situation like this, anything could happen.
You could easily lose your way in the dark.
注意：有些情况下，很难判定此处究竟是“能力”还是“可能”，这时can也会出现在肯定句，相当于may，即两个都可以使用。
I fit’s fine tomorrow, we can go fishing.
You can travel from London to New York in under 6 hours these days.
3. could/can和“请求许可”，即：approved possibility
多用于表示“请求”得到许可、征求意见的情况。这时，will、can、may也可以使用，而、对应的would 、could、might则更加委婉。另外在人称使用习惯上略有不同，如will、would多用于第二人称；may则用于第一人称。
Could you post this letter for me?
I wonder if we could borrow your lawnmower?
4. could/can和“have done”
后面接完成式，could have done肯定式表示“本来有能力做、但是没有做”；或推测过去可能发生过的事情，但语气较弱、把握不大；can（not）have done则只用于否定式或疑问式，表示“（过去）不可能发生过”。
You could have done better, but you didn't try your best.
This glass is cracked. Someone could have dropped it.
Can he have done such a foolish thing?
I could have told you, but I didn’t think you would listen.
It could have been Dan, but I’m not sure.
用适当的情态动词填空
Miss Fang __1__ (not) read for very long without getting a headache.Her mother told her that she __2__ go to the Health Service and see a doctor.“You __3__ see a doctor as soon as possible，” she said.“You __4__ need glasses.”
When Miss Fang had free time，she went to the Health Service.The appointment clerk said that the doctor __5__ see her at 3：30.
Miss Fang replied that she __6__ not be able to be there at 3：30 because she had a class then.“The doctor __7__ take you at about ten to four，” the appointment clerk suggested.
“__8__ I put you down for ten to four，or __9__ you rather come tomorrow？”
Miss Fang thought she __10__ (not) waste any more time.The teacher __11__ be unhappy if she asked for permission to leave the class a little early，as he was always so kind to everyone.And she replied，“I think I __12__ make it at ten to four.”Miss Fang went to the class.She asked her teacher，“__13__ I leave at 3：45 today？I __14__ have an eye examination.” As expected，the teacher said，“Yes，of course you __15__.”
答案 1.couldn't 2.should 3.should 4.might 5.could 6．would 7.might 8.Shall 9.would 10.shouldn't 11．shouldn't 12.can 13.May/Can 14.must 15.can
