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编辑点评： GRE阅读考试的材料，非常强调逻辑的关系，所以逻辑要点是大家在解GRE阅读题的时候的关键，本文就为大家例举了这样一篇逻辑短文，供大家参考和练习。 随着GRE阅读考试的难度日益增加，大家需要有针对性地进行练习，本文为大家例举的就是逻辑短文的练习，文末还附有答案，供大家更好地练习。 The determination of the sources of copper ore used in the manufacture of copper and bronze artifacts of Bronze Age civilizations would add greatly to our knowledge of cultural contacts and trade in that era. Researchers have 5 analyzed artifacts and ores for their concentrations of elements, but for a variety of reasons, these studies have generally failed to provide evidence of the sources of the copper used in the objects. Elemental composition can vary within the same copper-ore lode, usually because of varying admixtures of 10 other elements, especially iron, lead, zinc, and arsenic. And high concentrations of cobalt or zinc, noticed in some artifacts,appear in a variety of copper-ore sources. Moreover, the processing of ores introduced poorly controlled changes in the concentrations of minor and trace elements in the 15 resulting metal. Some elements evaporate during smelting and roasting; different temperatures and processes produce different degrees of loss. Finally, flux, which is sometimes added during smelting to remove waste material from the ore, could add quantities of elements to the final product. | 
