GWD 23-23

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

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

C.    but then it proved
unable to handle the increase in business, falling months behind in its paying

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

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

I am not very clear about the use of while, and the meaning of " alling months behind in paying"

thank y

in this case, but is more appropriate than while based on the meaning.

but is a conj, so the 'it' in C is not needed.

prove is parallel to become, so proving is not correct

then E is correct.

falling months behind in its payment to doctors and hospitals. means the company postpone its payment to doctors and hospitals for months. it is "doing' form to reflect what is happening along with the main stentance.