must变否定是什么,变一般疑问句是什么?

1,must做比须时,否定是must not或mustn't；表示推测时,通常与be连用,否定用can't be
2,must做比须时,反义疑问句用mustn't；如You must obey the school rules,mustn't you?
表示推测时,要用be或助动词do的相应时态；如：Tom must be in the school room now,isn't he?
Tom must have arrived yesterday,didn't he?