TOEFL Listening: ETS-TOEFL听力机经 - N39I1ERWKW5Q8M5IP$

Why does the professor mention oxide compounds in the regolith? A. To point out that multiple techniques might be required to extract oxygen from the various compounds. B. To propose that the trace amounts of oxygen in the Moon's atmosphere escaped from the regolith. C. To emphasize that the regolith is gray because of its high aluminum oxide content. D. To point out that lunar soil contains large quantities of oxygen.