I just realized why - your main 'head' question is 'which of the following.... NOT be described as a buffer solution'
Then, you have '0.20 M NaOH and 0.40 M CH3COOH' right before choices - this must be connected to another question. I answered to the 'buffer' related question. But question was probably asking something about the strength of acid and the base that is equivalent to '0.20 M NaOH and 0.40 M CH3COOH'
So, there are 2 different questions are involved - next time, please, don't confuse tutors with the head question. It's important.