问题
选择题
_______it comes to traffic rules, I often come across such cases ________the local drivers obviously know them but won’t follow them.
A．If; why
B．As; which
C．Once; as
D．When; where
答案
答案：D
考查连词及定语从句。When it comes to sth.当提及到……时候；第二空考查定语从句，先行词为cases，在定语从句中作地点状语，选D。
子中的几种或全部，①取少量该溶液，加入过量氢氧化钡溶液，产生白色沉淀，该沉淀在盐酸中完全溶解；②另取少量该溶液，加入氯化铵并加热，有剌激性气味的气体X产生，该气体能使湿润的红色石蕊试纸变蓝；③在做②实验后的溶液中，加入硝酸酸化的硝酸银溶液，有白色沉淀产生。