A:1H、3H、H+互为同位素
B:金刚石、石墨、C60互为同分异构体
C:CH4和异丁烷互为同系物
D:正戊烷和异戊烷互为同素异形体
— I'm sorry I ____ (leave) my exercise book at home.
— Don't forget to bring it to school tomorrow, please.
4-1=3