题目

—What were you doing when he ________“hello”to you?—I _______in front of the blackboard.A. was saying; read        B. was saying; was readingC. said; read                  D. said; was reading 答案：D通电分解水时，常在水中加少量的氢氧化钠或硫酸，目的是： ，小明同学用150克溶质质量分数8%的稀氢氧化钠溶液通电一段时间后发现溶质质量分数变为12%，则被分解的水的质量是 ．