为什么这里要用must be'Your sister will be here in less than an hour and we must be at the station to meet her.We are late already.'这里单单用must不行么

为什么这里要用must be'Your sister will be here in less than an hour and we must be at the station to meet her.We are late already.'这里单单用must不行么 must be和must have been有什么区别he must have been sleeping.为什么这里要用must have been而不用must be 英语 这里划线句子must 后面为什么要加be It must be teenagers having fun 为什么这里要用having而不用to have It must be teenages having fun 这里为什么要用having 而不用to have Attention must be paid to your pronunciation. 注意Attention must be paid to your pronunciation. 注意发音,为什么要用paid. All the players in the football team must be (trained)five time a week.这里为什么要用trained be grown up被动词态中为什么用be?it must be terrible to be grown up.这句话中be grown up中的be为什么不用is?这里没有什么条件要用be原形啊. 到底什么时候要加BE?什么时候用BEI must be the winner of this game.这里为什么要加BE 到底什么时候要加BE?我知道在must后如果有系动词就用BE 但就是搞不清楚什么时候才要加BE 为什么不说I must be the w it must be difficult to live without any money.这里用some为什么不行 Theory must be combined with practice.理论必须联系实际.请教这里为什么用过去分词combined? You must be on time.为什么要用be? You must be firm where you think yourself to be right.中为什么要用where啊翻译下句子的意思,这里where是什么用法啊, what is your name?your的be动词应该是are 为什么在这里用is? Thanks for your helping me这里为什么要用your Your must look after yours.中的your,为什么要用your? if your answers are not correct,you must correct then by yourselves.为什么 这里 两个correct都用原型 you must wash your hands hefore eating.为什么要用your?you must wash your hands before eating.为什么要用your？