If a Small Amount of a Strong Acid Is Added

If a small amount of a strong acid is added to buffer made up of a weak acid,HA,and the sodium salt of its conjugate base,NaA,the pH of the buffer solution does not change appreciably because

A) the K_a of HA is changed.
B) the strong acid reacts with A^- to give HA,which is a weak acid.
C) no reaction occurs.
D) the strong acid reacts with HA to give H₂A⁺.
E) the strong acid reacts with A^- to give H₂A⁺.