英文的問題?

must be 有命令成分,所以您可以说YOU MUST BE LISTENING TO ME!
must have有一定要有的意思,所以您可以说成是I MUST HAVE THE CALCULATOR FOR THE EXAMINATION.

must be 　　一定要做．．．．
must have　　一定要有．．．

eg: ...must be a polite girl....
...must have a bath before having dinner....

These just my answer. Hope I can help you! ^.^