adj.上上下下的;起伏的;来来往往的;变动的;
例句:
It's very hard to turn the wick up and down.
这灯芯很难旋上旋下.
Prices have gone up and down like a seesaw this year.
今年的价格像跷跷板一样时涨时跌.
He learned to walk safely up and down stairs.
他学会了安全地上下楼梯。