What makes an effective buffer solution

Which of the following combinations produces an effective buffer solution? (Select all that apply.)
HClO4 and NaClO4
KBr and HBr
NaF and HF
NH4Cl and NH3

And how do you tell?!

NaF/HF and NH4Cl/NH3(aq)

You need a weak acid and the conjugarte base, or a weak base and the conjugate acid.