题目

----- Look at the noisy kids !        -----  Haven’t you heard the saying “ when the cat is away , the mice ______  .” A. play               B. will play           C. are playing 答案：B钠的相对原子质量为23，它失去一个电子后，发生改变的是A.核内质子数B.电子层数C.元素种类D.相对原子质量减少1