TOEFL Reading: ETS-TOEFL阅读机经 - 580SM10776F4336ML$

According to paragraph 3, what is true about comets' tails? A. Their shape led early astronomers to draw false conclusions about the Sun. B. They consist mostly of ionized gases that had been blown out of the Sun. C. Radiation pressure and solar wind both play a role in their formation. D. Their dust content decreases as a comet nears the Sun.