干净: clean, neat...
免除: to prevent, to avoid, to excuse, to exempt, to relieve, (of a debt) to remit...
保持: to keep, to maintain, to hold, to preserve...
包子: steamed stuffed bun...
筛选: to filter...
妨碍: to hinder, to obstruct...
物体: object, body, substance...
极力: to make a supreme effort, at all costs...
平行: parallel, of equal rank, simultaneous...
山区: mountain area...
