根据汉语提示填出合适的情态动词(包括否定形式)
1、who______(可能）it be at the door?
2、you_____ ______ _______(不必）leave so early.
3、you_____ ______(必须）tell everyone the result.
4、bikes________(不准）be parked here.
5、does the teacher______ ______(必须）help tom finish the exercises?