[求助]关于and / but 前面有逗号的用法 拜托一下

20.    (25635-!-item-!-188;#058&002069)
        

我直接将正确答案覆盖到原题上，画线和有色底纹是疑惑处

The hognose snake puts on an impressive bluff, hissing
and rearing back, broadening the flesh behind its head the way a cobra does and
feigning repeated strikes, but it has no dangerous fangs and no venom, and eventually, if its pursuer is not cowed by
the performance, will fall over and play dead.

我记得PP2 语法笔记第56题
        有写道
        『当and连接两个独立子句,每个句子都需要有各自的主,动词』

对等连接词如果要连接两个独立子句前后应该结构对称
        是否只有如下两种表达方式? (假设前后主词相同)

(1) S1+V1 and V2…   

(2) S1+V1, and S1+V2 

但是prep的题型中不是就是(2)吗? but it has no…, and will fall over and play dead

为何,and后面的
            it 不见了? 按照句意
        and应该不是和the
hognose snake 平行吧
--------------------------------------------------

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.

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

答案是
        E
            

像这题but的用法
        也是少了主词  why ?
这样的结构在GMAT是成立的吗？
        这样句子是否完整?

请问白勇与法或是OG ,GWD 有其它类似的例子或是说明吗?

1.共用一个主语 it这种是最为科学的表达,加入it则代词会多余

2.并列过程中一般时态保持一致,但本题是做了一个假设,所以主句将来时,从句现在时,没有问题

3有相同题型的

可是我也常看到被连接的两个句子各自时态不同却没有用逗点隔开呀

究竟像and 或是but 这种连接词
        可不可以用
        , and +V这种省略主词的句型??

我真是给弄迷糊了呀

拜托
        NN们帮忙提示一下规则吧

谢谢呀