You are right that the answer is either "B" or "C." In Connell's short story, "The Most Dangerous Game," no struggle between rich and poor appears. Instead, both Rainsford and Zaroff are depicted as being well-to-do. Also, the only part of the story which supports a "superstitious tale" is the rumors which are heard regarding Ship Wreck Island.
Those two being excluded, the only two answers left are: B) a bitter attack on hunting and C) a deadly contest between two hunters.
As for answer "B," the story could be looked at as an attack on hunting. The absurdity of hunting could be shown by Zaroff's desire to hunt people given he has become bored with typical prey. Zaroff, instead, "creates" a new prey--man. Zaroff justifies this by stating that he needs a prey which can reason and man is the only animal which can do so.
That being said, while answer "B" could be justified, the better suited answer is "C." Both Zaroff and Rainsford are talented hunters. Both hunters are also at the top of their game. Zaroff decides to bring Rainsford into his game and the game becomes a deadly contest between the two very talented hunters.