You must't pack your school bag when you hear the fire bell.(保持原意)

问题描述:

You must't pack your school bag when you hear the fire bell.(保持原意)

当你听到火警铃响的时候,不要去收拾书包。

只要把mustn't改成don't就行

当你听见火警钟声响起时,切勿收拾书包后才逃跑