标题: 求教一题 [打印本页] 作者: mijianture 时间: 2011-5-25 15:21 标题: 求教一题 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.
when canals and eventually railroads reached into the region, there were substantial supplies of coal that was
once canals and eventually railroads reaching into the region, there were substantial supplies of coal having been
with canals and eventually railroads reaching into the region, there had been substantial supplies of coal
canals and eventually railroads reached into the region, with substantial supplies of coal being
as canals and eventually railroads reached into the region, substantial supplies of coal were