如何理解as在这句话中的作用？

xiao_s000

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.

                                 

1. as large, integrated companies such as Bethlehem Steel
2. as large, integrated companies, such as Bethlehem Steel, that
3. with large, integrated companies, such as Bethlehem Steel, that
4. while large, integrated companies, such as Bethlehem Steel, that
5. and large, integrated companies such as Bethlehem Steel

   Answer: B

答案是B ，请教一下，as 及其后面做什么成分？

linawanggta

AS 引导的原因从句吧，解释前面的The steel industry has changed radically。。好阴险啊，这么多逗号，眼睛一看花就选错了..