TOEFL Listening: ETS-TOEFL听力机经 - 91XN5F5F3OQDT69SP$

Why does the professor mention the duration of solar eclipses? A. To demonstrate the importance of the coronagraph as a research tool. B. To describe the effects of solar eclipses on auroras. C. To support a conclusion about the connection between sunspot cycles and other solar phenomenon. D. To explain why auroras are infrequent.