A solution containing which one of the following pairs of substances will be a buffer solution?

all the hydrohalogen acids EXCEPT HF are strong acids which mens their conjugate bases Cl-1, Br^-1 and I^-1 are WEAK bases, incapable of binding protons.In buffers the weak acid reacts with strong added base and the conjugate base of the weak acid reacts with the protons coming from added acid....So a combination of a strong acid and its conjugate base can NEVER be a buffer. HF is only partially ionized ( Ka ~ 3 X 10^-4 so its conjugate base F^-1 is a moderate strength base ( about 1/10th as strong as acetate ).