prep1-63一点疑惑

slamshady

Unlike emergency calls that travel through regular telephone lines, where they thus automatically inform the operator of the location and phone number of the caller, cellular calls require emergency operators to determine the location of the caller.
(A) lines, where they thus automatically inform the operator of the location and phone number of the caller, cellular calls require emergency operators to determine the location of the caller
(B) lines and thus automatically inform the operator of the location and phone number of the caller, cellular calls require emergency operators to determine the location of the caller
(C) lines, thus automatically informing the operator of the location and phone number of the caller, the location of the caller on a cellular phone has to be determined by the operator
(D) lines, and thus automatically inform the operator of the location and phone number of the caller, emergency operators have to determine the location of the cellular phone caller
(E) lines, thus automatically informing the operator of the location and phone number of the caller, emergency
operators receiving a cellular call have to determine the location of the caller

这里prep笔记对D的解释是：“ and前面有逗号,说明and后面应该是一个完整的句子,应该补出主语they,但这样会使得句子变得复杂,直接去掉逗号构成动词的并列更好”

有点不理解，为什么有了逗号，and后面就要补出主语they？真的有这样的说法吗？

jtrchina

That is correct,at lesat in Gmat.
The use of "and" can be classified as 2 ways:
1."and" without "," before indicates that a parallism exsists,which needs the formation of parallel parts to be identical.
2."and" with "," before adjoions 2 independent sentences,each including its own subject and verb,respectively.Here,there is only one exception:when a,b,c,and d appears,even though there is "," before "and",such form of sentence subjects to rule #1.
Hope it helps!

slamshady

嗯嗯。。。有道理，谢谢哈！