我们知道当and连接并列成分时可以省略相同成分。比如X do A, do B, and do C

我想知道当两句句子是用but/altough等表示转折的词时，可以省略相同成分吗？

我这里问的是but做conj的情况： but做介词(except) 当然可以省略（比如i am not a student but a teacher, i can't do A but do B)

把问题总结成一句话：X do A, but （X） do B （表示转折而不是except, 且but前有逗号。）这里的X可不可以省略？？？

 我查了longman，OG和白勇，没有发现省略的情况。但是做GWD题遇到了正确选项是省略的情况。

 GWD-23-Q23

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.

正确选项： but then proved unable to handle the increase in business, falling months behind in paying

"X became, but then proved..."

下星期就考了很急！谢谢！

谢谢！