The steel industry

dustystormy wrote: I am not able to understand the intended meaning of the sentence and therefore failing to eliminate option logically.

The intended meaning of the sentence is that
There is a change in way the steel industry is today
1.Earlier they used to be very large and had integrated involving process from mining and shipping and ideally would have involved more number of workers.
2.Today these companies have downsized and it is implied thay they are not so integrated(so mnay multiple processes)

This is best expressed by option B.

A is out because its a run on sentence misses that after Bethlehem Steel
B.Fine
C.with--doesnt provide a reason...which is best expressed by as
D.while is used for contrast or simueltaneous..The sentence explicitly states about the change so no contrast request.Also we are not contrasting anything here..Just speaking about the chage
E.--and is inappropriate..that is missing after Bethlehem steel.

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, such as Bethlehem Steel, that
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

GMATGuruNY wrote:

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, such as Bethlehem Steel, that
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

A and E: large, integrated companies...conducted...have greatly downsized
Here, a conjunction is needed to connect the two verbs (conducted and have downsized).
Eliminate A and E.

C: with large, integrated companies...have greatly downsized.
Here, the portion in red -- an independent clause, composed of a subject (companies) and a verb (have downsized) -- serves as the object of the preposition with.
An independent clause cannot serve as the object of a preposition.
Eliminate C.

Generally, COMMA + while serves to express a CONTRAST.
D: The steel industry has changed, while large companies have greatly downsized
Here, the clauses in red do not express contrasting ideas.
Eliminate D.

The correct answer is B.

The core meaning of the OA is as follows:
OA: The steel industry has changed, as large companies that once conducted operations from mining to shipping have greatly downsized.