A:Na+、SO42-、Ba2+、Cl-
B:Mg2+、K+、CO32-、NO3-
C:Na+、SO32-、NO3-、Cl-
D:Ca2+、HCO3-、Cl-、NH4+
英国发动鸦片战争的主要目的是( )
The World Health Organization gave a warning to the public without any ______when the virus of H1N1 hit Mexico in April, 2009.