原子中壳层电子吸收足够的能量脱离原子核的束缚变为自由电子的过程称为（）.
A.基态
B.激发
C.电离
D.跃迁
E.特征光子
参考答案：C
简述核被膜的主要功能。
—_____ did you write to your e-friend yesterday?
—For more than half an hour.[ ]
A. How often
B. How much
C. How long
D. How soon
