问题描述：
from one to five yesterday
The boy jumped up and down.
这男孩跳了一下
The boy was jumping up and down.
这男孩不停地跳着
jump up是跳 为什么要加一个down
The boy jumped up and down.
这男孩跳了一下
The boy was jumping up and down.
这男孩不停地跳着
jump up是跳 为什么要加一个down
问题解答：
我来补答展开全文阅读