TOEFL Listening: ETS-TOEFL听力机经 - X9E6NG32X5VAE6O1P$

According to the professor, what theories were proposed in the 1700s to account for the appearance of auroras? A. Auroras are caused by light refracting off ice and snow. B. Auroras are caused by CMES. C. Auroras occur when gases from sunspots hit glaciers. D. Auroras occur when an electric current between Earth's poles is disrupted.