In paragraph 5, why does the author include the information that the oxygen isotope ratio of the ocean changes as a great deal of water is withdrawn from it by evaporation and is precipitated as snow to form glacial ice? A. To explain how scientists were able to calculate how frequently the continental ice sheets expanded and contracted B. To explain how scientists have determined that there was no great change in ocean temperatures at the equator during past glaciations C. To provide evidence that oxygen-16 has a greater tendency to evaporate than does oxygen-18 D. To suggest that equatorial marine organisms absorb more heavy isotopes than do marine organisms elsewhere