Rewrite the following unbalanced equations, changing them into balanced net ionic equations (assume that all reactions are in water solutions):
a. H2S(g) + CdCl2(aq) ? CdS(s) + HCl(aq)
b. Zn(s) + H2SO4(aq) ? ZnSO4(aq) + H2(g)
c. AlCl3(aq) + Na3PO4(aq) ? AlPO4(s) + NaCl(aq)