能否给个TTGWD的讨论连接

能否给个TTGWD的讨论连接,我发现有些题目后面的的答案和老大说的讨论不太一样啊

谢谢.

Q19:

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.

1. while it then proved unable to handle the increase in business, falling months behind in its payment to
2. while it then proved unable to handle the increase in business and fell months behind in its payment to
3. but then it proved unable to handle the increase in business, falling months behind in its paying
4. but then proving unable to handle the increase in business, falling months behind in paying
5. but then proved unable to handle the increase in business, falling months behind in paying

不太明白什么意思,为什么是E?

这家公司成为最大的provider，但还是不能适应增长。。。用but

一般　its　or their　doing的表达方法是有问题的。。。