TOEFL Listening: ETS-TOEFL听力机经 - 1C1DW9QZVL6J6109P$

Why is the professor excited about the presence of ammonia on Titan? A. Ammonia may have been the result of atmospheric changes on early Earth. B. Ammonia was present in significant quantities on Earth when life first appeared. C. The presence of ammonia has motivated scientists to look for atmospheres on other moons. D. The presence of ammonia often coincides with a rise in oxygen levels.