D is the answer to this question. There are some people who learn how to react to different circumstances depending on what they are accustomed to do. For example, there are some people who may become afraid of the sounds that are heard when the mall is closing down because there are a lot of items that can make a lot of noise.
They may have associated the noise with something that they have already experienced in the past. There are also a lot of people who may find their mouths salivating when they smell something that they find pleasant. These are responses that people may be accustomed to doing.