must 应该，必须，一定
1) 表示出于职责、义务、主观意识而该做某事
We must protect people's rights .我们应该保护人民的利益。
Everyone must be loyal to his motherland .
每个人都应该忠于自己的祖国。
You must serve the people when you grow up .
你们长大成人时应该服务于人民。
Students must work hard at their study .
学生应该努力学习。
We must speed up the pace of our economic reform .
我们必须加速经济改革的步伐。
You must hurry up or you'll be late .
你必须得快点儿，不然会迟到的。
I have to go now for I've got a meeting 15 minutes later.我现在必须要走了，因为我15分钟后有个会要开。
He has to be back home by five to fetch his son from kindergarten .
他必须在五点钟前回家去幼儿园接他的儿子。
Jenny had to tidy up the room before her mother came back .
珍尼不得不在她妈妈回家以前将房间整理好。
We'll have to reconsider the whole thing .
我们将不得不重新考虑整个事情。
注意：在这种用法中，回答以must引导的问句时，若是否定答复，不可以用mustn't 而需要用needn't 或是don't have to，因为mustn't意思是"绝不能、一定不要"，而没有"不必"的意思。例如：
--Must we hand in our exercises today ? 我们今天必须交作业吗？
--Yes , you must .是的，必须交。
--No , you needn't (or , you don't have to ).
不，不必今天交。
3）表示禁止（用于否定句）
You must not speak ill of others .
你一定不要说别人的坏话。
Cars must not parked here . 这里禁止停车。
Smoking must not allowed in the office .严禁在办公室吸烟。
You mustn't talk to girls like that .你绝不能那样对女孩子说话。
4）表示猜测、推测must常用于肯定句中表示猜测。对现在或未来的事进行猜测时，后接动词原形；对已经发生的事进行猜测时，后接have + 过去分词。例如：
You must be tired after working so long .你工作这么久以后，肯定累了吧。
It must be that naughty boy crying outside .肯定是那个调皮的孩子在外面大叫。
The idea must be accepted by the society sooner or later.
这种想法肯定或迟或早会被社会所接受的。
It must have rained last night for it is so wet outside .
外面这么湿，昨晚肯定下雨了。
I didn't see you in class yesterday. You must have been
absent .我昨天上课没见着你，你肯定没有来。
