A:13C和14C属于同一种元素,它们互为同位素
B:6Li和7Li的电子数相等,中子数也相等
C:14C和14N的质量数相等,它们的中子数不等
D:1H和2H是不同的核素,它们的质子数相等
— The storybook is very interesting.
— I agree with you. I ______it twice already.