When one berth is placed over another, a dust-proof bottom should be fitted beneath the bottom mattress of spring bottom of the upper berth.
When one berth is placed over another, a dust-proof bottom should be fitted beneath the bottom mattress of spring bottom of the upper berth.
如使用双层床，上铺床垫下的弹簧床绷下方应垫上一层防灰尘的底板。