题目

高锰酸钾（KMnO4）中锰元素的化合价为 A．+1        B．+4        C．+6        D．+7 答案：D _____ the 9.3 million students are fighting for university seats in the testing rooms, their parents are experiencing a test of a different sort.    A. After          B. Until              C. Since                    D. While