Classify the reaction type : combination , combustion, decomposition , single displacement, or double-displacement
a) PbO2(s) ? Pb(s)+ O2(g) ___________________
b) C2H5OH(l) + 3O2(g) ? 2 CO2(g) + 3H2O(l) ___________________
c) 2Al(s) + 3CuSO4(aq) ? Al2(SO4) 3(aq) + 3Cu(s) ___________________
d) NaCl(aq) + AgNO3 (aq) ? AgCl(s) + NaNO3(aq) ____________________