TOEFL Listening: ETS-TOEFL听力机经 - 2JKPK40W663SV0V7P$

How do sunspots contribute to auroras? A. Sunspots increase the intensity of Earth's magnetic field at the poles. B. Sunspots emit charged particles that collide with atoms in Earth's upper atmosphere. C. Sunspots bombard Earth with oxygen and nitrogen atoms. D. Sunspots cause temperature changes at Earth's poles.