老Prep63 关于thus的用法

疏离无罪

63.(27901-!-item-!-188;#058&003440)

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

答案是b
A的where为什么不能理解成through which呢 这样意思也对啊
还有B的and thus表示因果关系结构 那请问各位NN thus还有些其他什么用法