The room must be aired请问1 为什么be要用原形? 2 must 本身就有必须的意思?为什么要跟个be? 就算must be是固定搭配,must 本身有必须的意思 不加be不可以吗?

We must keep the air in the room clean.(改为被动语态）The air in the room must ＿＿ ＿＿ clean. there must be someone in the room _(be)there It must be the country air 请问可不可以把the country air改成the country's air呢?为什么? The room ___ a stale air.It must have been vacant for a long time. She must be in the room.的意思 we must (be)quiet in the reading room. the room must be kept wet.变成被动语态! They must be in the reading-room,_______ _______[They must be in the reading-room,_______ _______[反义疑问句] 1.the doctor advised the room ____ A to air B to be air C to have been aired 2.,don‘t worry all the children___ by nurese A are well taken care of B take good care of C are taken good care of 3 .you ____the bus if you had got up A must catch B must You must air the room.(变为同义祈使句）————the————. the air in the room was still These magazines_____out of the reading-room A.must not take B.must not be taken C.must not take they must dust the room when were you air the room yesterday? air the room可以换成什么 The light in the room must be turned offThe light in the room must be turned off before you leave .为什么要用must be 不是填must turn off the room must be clean还是must be cleanedMother said to her daugther“The room ——— before you leave.. 28.---- The light is on.Who is in the room?---- _____ must be my sister.A.There B.It C.She D.That34.____the ground is ,___the air becomes.A.The high,the thin B.Higher,thinnerC.The higher,the thinner D.Higher,the thinner43.---- We will bulid a subway