In the following sets of reactants which two sets best exhibit the amphoteric character of ${\mathrm{Al}}_2{\mathrm{O}}_3\cdot \times {\mathrm{H}}_2\mathrm{O}$ ?

Set 1: ${\mathrm{Al}}_2{0}_3 . {\mathrm{xH}}_2\mathrm{O} \left(\mathrm{s}\right)$ and ${\mathrm{OH}}^{-}$(aq) 

Set 2:${\mathrm{Al}}_2{\mathrm{O}}_3 . {\mathrm{xH}}_2\mathrm{O}$ (s) and ${\mathrm{H}}_2\mathrm{O}$ (1) 

Set 3: ${\mathrm{Al}}_2{\mathrm{O}}_3 . {\mathrm{xH}}_2\mathrm{O}$(s) and ${\mathrm{H}}^{+}$ (aq) 

Set 4: ${\mathrm{Al}}_2{\mathrm{O}}_3 . {\mathrm{xH}}_2\mathrm{O}$ (s) and ${\mathrm{NH}}_3$ (aq