Among the given choices NH₃/NH₄Cl is the best choice to prepare pH = 9.0 because pKa of the salt of NH₄Cl nearly equals to 9 (pKb = 4.75, hence pKa = 14 - pKb = 14 - 4.75 = 9.25). A buffer can't change its pH +/- pKa, so this combination is best to prepare desired pH.
