GWD 4-17我对答案有一些置疑,大家看一下

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

答案B,为什么A不对呢?

首先我分析了一下句子结构, the industry has changed...as large integrated company such as ...have greatly downsized or (have) shut down together. 这样的话A,once conducted operations...at the other做such as BS的定语从句,并且省略that,不对吗?为什么这里一定要用逗号+that呢?难道是为了使 such as BS变成同位语,然后that跳过去修饰companies?

疑惑多多,请指教