what goes up ang down but doesn't move?

what goes up ang down but doesn't move? what goes up and never goes down? what comes down but never goes up- what goes up but never comes down what goes up when rain comes down what goes up must come down What goes up,must come down 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 goes upill ang downhill ,and always stays in the same place?求英文答案. what goes up but never comes up猜一猜 英语IQ题：what goes up but never comes down? what comes down,but never goes up?先英翻中再解题 What thing always goes up,and never comes down what goes up and down but doesn't move? 是什么意思? what alway goes up,but never come down? what goes up and down the stairs without moving?