It goes up and down ,in and out ,front and back ,sometimes'中文意思?

what goes up and never goes down? What is it that goes up and never goes down ?请帮忙猜一下那是什么? a---- goes up and never goes down How good it is to be always young It goes up and down ,in and out ,front and back ,sometimes'中文意思? he goes up and down翻译 What always goes up and never goes down? What always goes up and never goes down?是什么意思? What always goes up and never goes down? what is it that goes up and goes down but does not move?求大神级回答 句子 猜谜语：What is more useful after it is broken?还有一个：What goes up and never goes down? 英语翻译What always goes up and never goes down?What’s black when it's clean and white when it's dirty? What thing always goes up,and never comes down what goes up and down but doesn't move? 是什么意思? she goes up and down the building by lift Which thing always goes up,and never comes down?是什么? what goes up and down the stairs without moving? shake it up and down什么意思 17.Little water drop feels very hot.So it _______.A.falls down B.goes up C.goes down