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问题: 情态动词的否定

you need not come until six 什么时候用must need呢??? 怎么区别使用呢???
you must not paly near the road
she has to help me every day他和下面一句有什么区别??? has to 和had to 的意思有区别吗??
she had to help me last night
may 的否定形式是怎么样的??

解答:

you need not come until six 你没有必要来在6点钟之前.这里,"need"解释为必要.
相比之下,must语气更强,一般解释为一定,必须.最好能结合语境来选择.

has to ,had to两者只是时态不同
has to/had to与must都有必须的意思,但是前者是客观的,后者主观色彩更重

may 的否定形式:一般情况下may not