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小石头的家住在15层,因此每天要乘电梯上下楼。假如没有电梯的话?唉!想起来都头晕。不过,电梯是怎样来回升降的呢?
Small stone home lives in the 15th floor, so every day to take the elevator up and down. If there is no elevator? Alas! However, the elevator is how it back and forth?