题目

If Mr. Dewey _____ present, he would have offered any possible assistance to the people there. A . were B . had been C . should be D . was 答案：B有A、B、C、D四种溶液，它们是烧碱、硫酸、碳酸氢铵、氯化铜溶液中的某一种。各取少量，将其两两混合，其中A、B混合有蓝色絮状沉淀生成，C与足量B或D混合均有无色气体产生。根据题意回答下列问题：（1）B、C分别是______________、___________________。（2）向A中滴加B，离子方程式：_____________________。向C中滴加D，离子方程式：_____________________。（3）少量B和C混合，现象：_______________，离子方程式：__________________。