A, according to the carbonate ion and hydrogen ion will generate water and carbon dioxide, can't coexist, so a is impossible;

B, chloride ion and other ions will not react and can coexist, so b may;

C, sulfate ion and other ions will not react and can coexist, so C may;

D, nitrate ions and other ions will not produce precipitation, gas and water, but they can coexist, so D is possible.

So choose: a.