The correct option is C anything / nothing
The first sentence shows a genitive case is when we add apostrophe S (’s) to show possession, that something belongs to another or a type of relationship between things. In the second sentence, it is inferred that the person involved doesn't have any money. Therefore using logic we understand it's not possible for him to buy anything. Thus 'nothing' is the correct option that is the option C. Option B is ruled out as it is not possible for someone to buy something without possessing any money. Option A is ruled out as anything means at least one or more but the person B it is referred that he doesn't have any money. Similarly, Option D is discarded because it refers to one or more persons.