题目

Nowadays with the increasing popularity of cars, people are taking ______ exercise a day as they did in the past. A . half as much B . as half as C . less than half much D . as half 答案：A明矾可做净水剂是因为                                        ，有关的离子方程式为                              ；向明矾的水溶液中加入饱和的小苏打溶液，则观察到的现象是         ，有关的离子方程式                                  。