请教TTGWD-4-Q17

The steel industry has changed radically over the last two decades, as large, integrated companies such as Bethlehem Steel once conducted operations from mining at one end of the process to shipping at the other have greatly downsized, or in some cases shut down altogether.

A.      as large, integrated companies such as Bethlehem Steel

B.      as large, integrated companies, suc as Bethlehem Steel, that h

C.      with large, integrated companies, such as Bethlehem Steel, that

D.      while large, integrated companies, such as Bethlehem Steel, that

E.       and large, integrated companies such as Bethlehem Steel

答案选B，请问as缘何而来呢？

as “随着。。”这里是连词，后面接句子