You mustn't pack your school bag when you hear the fire bell.保持原意怎么改?这句话我不懂,回答的,顺便也把它的意思写出来吧,还有保持原意的句子.

You mustn't pack your school bag when you hear the fire bell.保持原意怎么改?这句话我不懂,回答的,顺便也把它的意思写出来吧,还有保持原意的句子.
You mustn't pack your school bag when you hear the fire bell.保持原意怎么改?
这句话我不懂,回答的,顺便也把它的意思写出来吧,还有保持原意的句子.

You mustn't pack your school bag when you hear the fire bell.保持原意怎么改?这句话我不懂,回答的,顺便也把它的意思写出来吧,还有保持原意的句子.
You mustn't pack your school bag when you hear the fire bell.
当你听到火铃响的时候禁止收拾书包
You can't pack your school bag when you hear the fire bell

没有听到火警铃声决不能打包

听到火警的时候一定不能归书包。（赶紧逃）