然而，样品制备过程中可能带入人为的物质。
However, it may arise from an artifact during sample preparation.
国会对廉价出售的后果一无所知：全球氦气价格被人为压低，以至于几乎没有人愿意回收这种物质或明智地使用它。
The Congress is ignorant of the consequence of fire sale: global helium prices are so artificially deflated that few can be bothered recycling the substance or using it judiciously.
古代石器时代的人类化石，文物和人为动物的物质非常丰富。
The material of human fossil, culture relic and zoolite in the Old Stone Age are very abundant.
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