问题补充：
The place the bridge is supposed to be built should be the cross-river traffic is heaviest.
A. which; where
B. at which; which
C. at which; where
D. which; in which
答案：
A. which; where
B. at which; which
(答案→)C. at which; where
D. which; in which
解析：考查定语从句和表语从句：句意：桥梁应该建在水上交通最拥堵的地方。根据句子的意思可知，第一个从句应该是定语从句，先行词为the place，在从句中作地点状语，故排除A、D；第二个从句应该是表语从句，从句中缺地点状语，用where，in which引导的是定语从句，故排除B。选C。
