vegetable, three, woman, question, his
甲
乙
丙
丁
A
H2SO4
NaOH
NaCl
Na2CO3
B
CO
CO2
CuO
C
Fe
Fe2(SO4)3
Mg
HCl
D
O2
已知:a=12-3,b=12+3,则a与b的关系是( )