请解释为什么第一个must后面加be 而第二个must后面没有加beShe knows that a secretary must be pleasant and helpful nomatter how busy she is.She knows she must keep calm if a caller gets impatient or becomes angry.

请解释为什么第一个must后面加be 而第二个must后面没有加beShe knows that a secretary must be pleasant and helpful nomatter how busy she is.She knows she must keep calm if a caller gets impatient or becomes angry. something must be done to pretect our enviroment.must后面为什么接done.而不能接doing请详解哦 英语 这里划线句子must 后面为什么要加be must be后面可以加动词吗 为什么would like后面加to be而will后面加be呢? 情态动词如must ,could ,would等等后面什么时候加be动词?In law,you needn't to answer these problems.I needn't type this report today.情态动词后面不是加动词原形吗。为什么第一个句子要加to 第二个句子不加to will 为什么后面加动词原形,而be willing后面为什么加动词不定式 It___cold.You'd better wear warm clothes.A.may B.maybe C.may be D.must如确定答案正确请做适当解释.为什么有的表猜测的情态动词后面有be,而有一些没有?例：①It might snow.②It may be cold and wet in Hong Kong in Janua There must be a dog sitting behind it .为什么sit 后面加ing must后面能不能加not,为什么? 关于情态动词的问题1、She may lose her way.We must stay here.2、They can be friendly.He could be here soon.为什么 1 的两句话不加be ,而 2 中的两句话要加be情态动词到底什么时候后面要加be,什么时候不加 雅思听力单复数为什么高中老师教one of the 后面的名词是加s但是剑桥6T3 第21题the students must investigate one part of the后面是写entertainment industry,而不用复数? must be后面是动原吗 must be后面是动原吗 Be very careful and live very quietly.动词后面不是要跟副词么,为什么第2个very跟了 而第一个very没跟 must be后面跟什么词You must be early tomorrow.这句话在must be 后面加early对吗?应该加什么形式的词语? She must be at least forty .为什么要在must前加be?must后加be I'll be right back.和I'll is right back.第一个为什么要加be而第2个用ISby the way:什么时候加be啊,最好一针见血 说的好我会加分的