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| 1. | The ventilation of a sewer is vital to prevent the concentration of dangerous and offensive gases and |
| 排水系统的通风对于防止危险有害气体的积聚和管内水位的忽涨忽落非常重要。 |
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| 2. | The concentration under reduced pressure brings short time of concentration and prevent the destruction |
| 由于采用减压浓缩，故浓缩时间短，且不会破坏热敏性物料的有效成份。 |
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