A:Ag+、Ca2+、Cl-、NO3-
B:K+、NH4+、CO32-、OH-
C:Na+、Cl-、CO32-、OH-
D:H+、K+、CO32-、NO3-
In April, 2009, President Hu inspected the warships in Qingdao, ______ the 60th anniversary of the founding of the PLA Navy.