A.10~20mL B.20~30mL C.30~40mL D.40~50mL
A.>1% B.<0.01% C.0.01%~1% D.0.01%~0.001%
A.HNO3+H2SO4(1:3) B.H2SO4+HCl(3:1) C.HNO3+HCl(3:1) D.HCl+HNO3(3:1)