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

我想问一下, , D是有明显的错, ABC 怎么错了, 是不是转折句要省略主语,所以ABC错了,哪位可以帮解释一下, 多谢!

E the best 

E 没有it，所以不需要.回答的不好，只是我的感觉

希望有人更清楚地回答