It’s a long time__________I saw you last. Yes, and what a pity it will be a long time__________we see each other again. A. before, since B. when, when C. since, before D. when, then 答案:C日常生活常接触到“含氟牙膏”、“高钙牛奶、碘盐”、“富硒茶叶”、“加铁酱油”等用品,这里的氟、钙、碘、硒、铁指的是( )A. 单质B. 元素C. 离子D. 原子