题目

On the first day of the 11th grade, our new math teacher Mr Washington asked me to go to the blackboard to do a math problem. I told him that I couldn’t do it. He asked, “Why not?” I paused, and then I said, “Because I’m educable mentally retarded (可教育智能迟滞).”    He came from behind his desk and looked at me. “Don’t ever say that again. Someone’s opinion of you does not have to become your reality,” he said.     It was a very special moment for me. Doctors said that I was educable mentally retarded in the fifth grade, and I was put back into the 40℃时将含有少量未溶解的Ca(OH)2的饱和石灰水，降温到20℃，使之变成不饱和溶液，这时溶液中溶质的质量分数 [　　] A．增大 B．减小 C．不变 D．无法判断