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. Promptness on the job is a must.Comfortable shoes are a must when taking a walking tour of Wales. 工作上准时是绝对必要的.步行去威尔士旅行时舒服的鞋是绝对必要的物品 n.attributive.（定语名词） Often used to modify another noun: 常用来修饰另一个名词： a new book that is must reading; a list of must legislation for the session. 一本不可不读的新书；开庭不可缺少的立法一览表
