OG10-105的句子结构看不懂？

105.
            An inventory equal to 90 days sales is as much as even the strongest businesses carry, and then only as a way to anticipate higher prices or ensure against shortages.

(A) as much as even

(B) so much as even

(C) even so much as

(D) even as much that

(E) even so much that

答案是A，我的问题是第二个分句，and then only as a way to anticipate higher prices or ensure against shortages.在这里表示什么成分，是不定式作定语么，为什么and前面要加一个逗号呢，如果去掉这个逗号可不可以呢；

请同学们赐教；

问得好，当时我只看前半部分和解题紧密相关的了。

An inventory equal to 90 days sales is as much as even the strongest businesses carry, and then only as a way to anticipate higher prices or ensure against shortages.

从逻辑意思上说，前后两个clause是并列关系。逗号+and连接两个并列分句，判断and后分句应该是主语蒙前省，be动词相应省略了。完整结构是：

An inventory equal to 90 days sales is as much as even the strongest businesses carry, and then it is only as a way to anticipate higher prices or ensure against shortages.

BY语法上说 then,also,there,however等副词不能代替and起连词作用。就是说连词and 一定要出现。

在此,句1，and then+句2（省略句1中的相同主谓）

感谢楼上两位的解答，再请问一下，

1.因为逗号＋and表示两个分句，而这里两个分句的主谓都相同，可不可以不用逗号呢，

An inventory equal to 90 days sales is as much as even the strongest businesses carry
            and then it is only as a way to anticipate higher prices or ensure against shortages.

2.如果可以不用逗号，那在不用逗号的情况下省略第二的分句的主谓可以么，

An inventory equal to 90 days sales is as much as even the strongest businesses carry and then only as a way to anticipate higher prices or ensure against shortages.
            

3.还有，如果可以省略逗号，那么原句却使用了逗号，加上这个逗号的好处是什么呢；

实在是麻烦了，只是想在逗号和and上较一下真，因为遇到了好多类似情况，很困惑；

我个人感觉有逗号两个分句会比较清晰，并不易前面的修饰成分产生歧义。但没有依据，请NN指教~~

说一下我的感觉, OG中是规定 and如果接与其前面不同的主语时, 一定要加逗号, 相反的情况时如果主语相同, 那么是不需要加逗号的.

但是上面说的第二种情况有例外, 有的时候如果第一个主谓较长, 那么and+第二个谓语仍然用逗号隔开