In the following sets of reactants which two sets best exhibit the amphoteric character of Al₂O₃·xH₂O?

Set I: Al₂O₃·xH₂O(s) + OH⁻(aq)
Set II: Al₂O₃·xH₂O(s) + H₂O(l)
Set III: Al₂O₃·xH₂O(s) + H⁺(aq)
Set IV: Al₂O₃·xH₂O(s) + NH₃(aq)