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In the 1820's, anthracite coalfields opened in eastern Pennsylvania, and when canals and eventually railroads reached into the region, there were substantial supplies of coal that was exported to the nation's growing mills, forges, factories, and railways.
  • Awhen canals and eventually railroads reached into the region, there were substantial supplies of coal that was 分析该选项
  • Bonce canals and eventually railroads reaching into the region, there were substantial supplies of coal having been 分析该选项
  • Cwith canals and eventually railroads reaching into the region, there had been substantial supplies of coal 分析该选项
  • Dcanals and eventually railroads reached into the region, with substantial supplies of coal being 分析该选项
  • Eas canals and eventually railroads reached into the region, substantial supplies of coal were 分析该选项
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正确答案: E
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