The author of the passage mentions black holes in order to provide A. an instance of a factual error to which popularizations of science are prone B. a metaphor for the emptiness typical of most popular science writing C. a case in which a metaphor for a scientific process leads to a misunderstanding of that process D. an example of the metaphorical explanations the author believes are typical of bad science writing E. an illustration of a complex phenomenon for which most readers require simplified explanations