题目

He ______ at once when I promised to help him.   A. cheered up      B. gave up    C. lighted up      D. turned up   答案：A已知某无色透明溶液中存在较多的Na+、OH-和NO3-,则该溶液中还可能大量存在的离子是A. CO32- B. Cu2+ C. Ca2+ D. NH4+