What purpose does the discussion about the Bering Strait in paragraph 2 serve in the passage? A. It explains the idea that changes in coastlines do not necessarily result in significant alternations to existing marine life. B. It illustrates the kind of impact that variations in land availability caused by climate change can have. C. It provides a large amount of archaeological evidence that casts doubt on changes in sea level during the Paleolithic period. D. It shows how ancient coastlines can serve as useful models in understanding recent changes in coastlines.