涛涛４－１９题希望大家帮帮忙啊

牧心

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

我不太明白此处while 与 but有何区别啊，平时使用的时候要如何区分呢

另外Ｃ选项有何错误啊

yushuang5555

答案是什么？？b吗？

牧心

答案是E