A:I understood
B:had I understood
C:did I understand
D:I had understood
将16克CO和CO2的混合气体通过灼热的氧化铁后,得到的气体全部变为CO2,且气体的质量增加到24克,则混合气体中CO2的质量为多少克?(提示:用差量法解)
7+3=____
14+5=____
17+3=____
12+7=____
18+2=____