题目

 —How terrible it is today!—      . A very bad day for swimming, isn't it?        A. So it is             B. So is it          C. Nor it is                        D. Nor is it 答案：A钠原子的原子核中有11个质子和12个中子，钠原子的核外电子数为(　　)A. 23 B. 11 C. 12 D. 1