OG207,请NN来确认关于逗号的用法

207. In the textbook publishing business, the second quarter is historically weak, because revenues are low and marketing expenses are high as companies prepare for the coming school year.

(A)            low and marketing expenses are high as companies prepare

(B)            low and their marketing expenses are high as they prepare

(C)            low with higher marketing expenses in preparation

(D)            low, while marketing expenses are higher to prepare

(E)            low, while their marketing expenses are higher in preparation

答案没有问题

可是A中间and前面为什么没有逗号啊，这不就是传说中的run-on sentence了吗

看OG菜鸟手册上说:从句中出现这种情况不用！！！

真的是这样的么?有请NN前来确认,多谢

因为and这个句子在从句里, 如果加了逗号看起来不知道该是谁的并列了, 即为了大局-主句的完整, 可以不用逗号.

我猜想，是不是当and前后的句子比较简单的时候可以不用逗号？

不是，句子并列的时候无简单、复杂之分；该题主要是连接的是两个because从句，相当于两个状语成分，and后省略了because，所以不需要用逗号隔开

as在这里是不是作为连词,相当于because ?

和as high as完全没有关系.