l must be to work和l must to work 哪个对,为什么加be

Must如果当助动词用,后方加的是不带TO的不定式。Must do sth。如果用作名词,句型就不是这样写,应该是：It's a must to do sth。所以你这边表达都不对 应该表达为l must work 这边的must是助动词 再问： must be 这种句型怎么用？谢谢 再答： 这时候的must还是助动词 表示必须 这时候的动词是be动词 1,English must be studied to get good grades。 2,Rooms must be cleaned to keep healthy。 3,Books must be read to gain knowledge。 4,Children must be educated to grow up。 5,Cotton-padded clothes must be woren to keep warm。 6,Buses must be taken to go to outskirts。 7,Trees must be planted to greening。 8,Mood must be cooled off to thinking。 9,Cellphones must be used to communicate。 10,Bags must be used to contain things。