Final answer:
The best buffering system among the options provided is CH₃CO₂H + CH₃CO₂K, as it consists of a weak acid and its conjugate base which can resist changes in pH.
Step-by-step explanation:
A buffer is a solution that resists changes in pH when small amounts of acid or base are added. The best buffering system among the options provided is option b: CH₃CO₂H + CH₃CO₂K. This is because it consists of a weak acid (CH₃CO₂H) and its conjugate base (CH₃CO₂K), which can effectively resist changes in pH.