Thanks for the question! So we’re asked here for what the main point of passage B is. (D) tells us that the main point is to tell us that Cather’s impressionistic narratives served as an important impetus for the development of narratology in the 1960s. However, is this even true? We’re told that Cather’s ideas anticipate narratology (in lines 35-36), but we are never actually told that her works served as an impetus or otherwise directly influenced the development of narratology. Since that goes beyond what passage B even states, it can’t be the main point, and so (D) cannot be the correct answer.
Hope this helps! Feel free to ask any other questions that you might have.