Where do astronomers think the elements other than hydrogen and helium in the atmospheres of white dwarf stars originated? Choose one: A. from the leftover materials from the planets in the star system that were "swallowed up" when the star was previously in giant stages B. from asteroids drawn in by the intense gravity of a white dwarf C. from rogue planets drawn in by the intense gravity of a white dwarf D. from metals that are stripped from the nearby planets of the star system