prep sc-63

wakesleep2011

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
我知道答案就在a,b之间，关键之在lines后面，我明白用where来修饰lines有些说不通。但是又是一个and thus ,不用再在前面加that吗，两个比喻从句呀。。。。a中用where有什么明显的不对马？