1. This new technology promises to keep food products moving smoothly on and off supermarket shelves, which will help keep overhead down and prices stable.
    这种新技术可望使在超级市场里的食品上下货架顺利进行，这将能降低管理费用，保持价格稳定。

2. You have to replace the books on the shelves before you leave.
    你离开之前必须把书放回书架上。