Can you come to my party?

can, could（能）

表示一般现在时和一般过去时两种时态，有时也能表示将来时。所有其他时态（包括将来时）须用to be able 加动词不定式来表示。

①What can I do for you?我能为你做什么吗？

②It surely can't be eleven o'clock already. 不可能已经十一点钟了。

③We were sure that he could pass the test.我们肯定他能通过测试。

④Will you be able to finish the chemical experiment today? 你今天能做完这个化学实验吗？

⑤The seventy-year-old man has been able to swim in the ocean in winter for twenty years.这位七十岁的老人冬天能在海里游泳已经有二十年的历史了。

must必须，应当

①You must get to the airport before nine o'clock. 你必须在九点以前到达飞机场。

②Your homework must be clear and complete.你的作业应当清楚完整。

③He must be in the reading room now.他现在准是在阅览室。（表示说话人对事物的推测）

④She must be writing a letter to her mother. 

她现在一定在给她妈妈写信。（must加动词不定式进行时也可表示对现在发生的动作的推测，表示“一定”或“准是”的意思。）

⑤The road is wet. It must have rained last night. 

马路湿了，昨晚一定下雨了。（must加动词不定式的完成式，说明对过去事物的推测，表示“一定”或“准是”的意思。）

●两种否定式的比较

must not表示“不应该”、“不许可”，语气比较强烈。如：

We mustn't waste our time.我们不应该浪费我们的时间。

need not（不必）表示must在意义上的否定。如：

Must we clean our classroom today?----No, you needn't.我们必须今天清扫教室吗？——不，不必。

have to（不得不，必须）

①To launch satellites into space, we have to use big powerful rockets.要把卫星射入太空我们必须得使用巨型强力火箭。

②There is no bus to the village and we have to walk there.没有到那个村子的公共汽车，我们必须步行去那里。

5、need需要

用于疑问句及否定句，单数第三人称不加-s，后接动词原形。（在肯定句里既可用做情态动词又可用做实义动词。当用做实义动词时，单数第三人称加-s，并有时态变化。）

①Need we go to the factory on foot?我们今天需要步行去工厂吗？

②You needn't do your homework in class. You may do it after class. 你不必在课堂上做作业，你可以课后做。

●needn't后加动词的完成式时，指过去已做了但不需做的动作。

③You needn't have bought the new watch, as the old one could be repaired.你本可以不必买只新表，因为旧表能修好。

④You needn't have brought your umbrella． It is going to be clear up.你本可以不必带伞，天就要晴了。

●didn't have to和didn't need to表示过去未做也不需做的动作。如：

⑤I didn't have to help her with her mathematics, for she is good at math.我没有必要帮她数学，她擅长数学。

⑥She knew the way to the library, so you didn't need to show her the way.她知道去图书馆的路，所以你没有必要给她指路。

—Mum,         I go out to play?—Yes, you can. But you must finish your homework first.

—       you use microblog(微博) to post messages?—Sorry, I        .

There’s only one day left(剩下). You         finish your school work by tomorrow(明天以前).

When winter comes,         spring be far behind?(冬天来了，春天还会远吗？)

—        I swim here?—I’m sorry. Children          swim alone(单独地) here.