yeh.. this is how i approached the question..
*buffers comprise of a weak acid and its conjugate base, so there goes A and C
*B is wrong cuz it isn't even the conjugate
*thus the answer is D
buffers dun hav to be diprotic
yeh.. i found it odd too.. i couldn't find many techniques in all the texts.. the deepest one i rkn was the third one but argh..not many techniques that i could see besides like.. 'descriptive language' and use of 2nd person