I had to work when I was your age．
②must只有一种形式，have to 则涉及人称、时态等方面的变化形式。
③二者的否定意义大不相同。如：
You mustn't go．(带有很强的语气)表示\禁止、不允许\
You don't have to go．(表示\不必\
④询问对方的意见时应用
must，如：
Must l clean all the room? e. 三个否定式
can’t /couldn’t不可能
needn’t 不必要mustn’t 不准
6. need
a.需要，必须 作情态动词，只用于否定句和疑问句。 ---Need I leave now?
---Yes, you must. /No, you needn’t.
You needn’t hurry.
You needn’t have taken a taxi.
He needn’t buy such an expensive coat.
didn’t need to do 过去没有必要做，也没有做 needn’t have done b. 常作实义动词、行为动词，有时态、人称和数的变化.可以接名词，不定式和动名词作宾语
(1) need+N .
They are certain to need
help. /I need no explanation. need no further discussion (2) sb. need(s) to do sb. doesn’t need to
My father needs to have a good rest.
They did not need to arrive so early.
=They needn’t arrive so early.
(3)Sth. need doing某事需要被做=sth. need to be done.