题目

. ___________    the classroom, the students went to the playground to watch the football match A. To clean            B. Having cleaned       C. Cleaned                                  D. Cleaning 答案：B下列说法正确的是（　　）A．NaCl是电解质，所以NaCl可以导电B．CO2能溶于水，且水溶液能导电，所以CO2是电解质C．BaSO4难溶于水，故将BaSO4放入水中存在电离平衡D．NaHCO3仅能在水溶液中导电