求助：GWD 28-20

states as following:

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.

A.      when canals and eventually railroads reached into the region, there were substantial supplies of coal that was

B.      once canals and eventually railroads reaching into the region, there were substantial supplies of coal having been

C.      with canals and eventually railroads reaching into the region, there had been substantial supplies of coal

D.      canals and eventually railroads reached into the region, with substantial supplies of coal being

E.       as canals and eventually railroads reached into the region, substantial supplies of coal were

答案是E，可是supply如何被exported呀？？？我觉得答案应该是A，虽然那个that was很讨厌，可是修饰coal是没有问题的。

there be...that be太过wordy

我个人感觉这里的主语还是coal. coal是supplies of coal的核心词..不知道可不可以这样理解

望NN出来看看