A:有大量SO 32− 溶液中:Na+、NH4+、SO 42− 、NO 3−
B:强碱性溶液中:NH4+、Ca2+、NO 3− 、Cl﹣
C:强酸性溶液中:Cu2+、Mg2+、HCO 3− 、SO 42−
D:有大量Ba2+溶液中:K+、Ca2+、CO 32− 、SO 32−
I've not seen him for a long time. He becomes stronger and more polite .
若关于x的不等式(1﹣a)x>2可化为x>21-a,则a的取值范围是 ____