Biology midterm: buffering agents?

okay. so again i missed this question too. haa:] but yeah. question is: WHY DO CELLS NEED BUFFERING AGENTS? A. to maintain constant internal environment at a ph of 10 || B. to function properly in an extremely basic internal environment.|| C.to function properly in extremely acid environment|| D. to minimize the changes in ph of the internal environment.|| I circled A and got it wrong. which answer is right and why?