A. while it then proved unable to handle the increase in business, falling months behind in its payment to
B. while it then proved unable to handle the increase in business and fell months behind in its payment to

D. but then proving unable to handle the increase in business, falling months behind in paying

but then proved unable to handle the increase in business, falling months behind in paying

C. [b]but then it proved unable to handle the increase in business, falling months behind in its paying doctors and hospitals [/b]

After several years of rapid growth, the healthy care company became one of the largest health care providers in the metropolitan area, [url]while it then proved unable to handle the increase in business, falling months behind in its payment to [/url]doctors and hospitals.

A. while it then proved unable to handle the increase in business, falling months behind in its payment to (it? metroploitan area or company)
B. while it then proved unable to handle the increase in business and fell months behind in its payment to (it? metroploitan area or company)
C. but then it proved unable to handle the increase in business, falling months behind in its paying (it? metroploitan area or company)
D. but then proving unable to handle the increase in business, falling months behind in paying ('but' onwards a clause should follow, not a phrase)
E. but then proved unable to handle the increase in business, falling months behind in paying

OA is E
why not A?

If you put C in the underline part and then read out the sentence you will find that the non-underlined part following the underlined part won't just fit in idiomatically

Hope this helps

i guess the problem with C is not "it" ambiguously referring to the company or the metropolitan area. "it" logically and unambiguously does refer to the company.

i guess the problem with C is not "it" ambiguously referring to the company or the metropolitan area. "it" logically and unambiguously does refer to the company.

the problem is in the part "falling months behind in its paying doctors and hospitals"

=>seems to say the company lags behinds in its doctors and hospitals that pay. paying seems to modify doctors and hospitals.

Mohit asked me to address this one.

In this context, "while" = "at the same time as" but that's obviously NOT what's being described, so eliminate A and B.

Then, we have parallelism!

the company became X, but then <it proved / proving / proved> Y.

The subject "the company" applies to both verbs. ("but" is the parallelism marker.) So, which is parallel to became? Proved. Eliminate C ("IT proved" - we already have the subject; we don't need a pronoun) and D (proving = not parallel to became).