Definition: You are given a question on high school chemistry. You are also given 4 answer options (associated with "A", "B", "C", "D"), out of which only one is correct. You need to answer the question by selecting the correct option. You should only answer with the choice letter, not the whole answer.
Input: To prepare a buffer, all of the following are needed except
(A)an acid with a pKa close to the desired pH (B)a conjugate acid along with its conjugate base (C)a buffer capacity sufficient to react with added acid or base (D)triple-distilled water

D