Word of mouth is the type of mode of communication when the details/information about a product/service/event etc. continues to spread from one person to next and so on through verbal communication.
Popular culture is the culture based on taste of ordinary mass and not a specific group of people.
Advertisement is synonymous with promotion of product/ services through types of media including print/ audio/ television/ internet website etc.
Thus, when people talk about their purchase of a product from a store, the name and information about the store spreads and more and more people become aware of the store.
Therefore, this is an example of “b. Word of Mouth”