GWD19里一道题，很纠结

self346959851

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E.

但是不懂。。。 and前后要平行，那么E里的as和什么平行呢？

boystar

as canals and eventually railroads reached into the region(during canals and eventually railroads reached into the region) 和In the 1820’s平行

糊涂的小黑

逗号之后部分，有强调的意思，我是按逻辑做的