Answer:
At that time the sound of the buzzing bee was most clearly a B. neutral stimulus.
Step-by-step explanation:
In Classical Conditioning, the stimulus can be unconditioned, neutral and conditioned and they provide responses (unconditioned and conditioned).
A neutral stimulus, as the name states, does not create a response on its own. It doesn't mean anything by itself until it is paired with another stimulus in order to become a conditioned stimulus and provide a response.
In this case, the buzzing sound means nothing to Sara because it didn't cause anything, it was just a neutral stimulus.