GRE Reading Comprehension: JiJing 352-GRE阅读机经352篇 - 0VT4LM6KXIR0I21IJ

According to the passage, astronomers' belief that comets are pristine relics was A. overturned by analysis of what happens when comets approach the Sun B. supported by what observations revealed about the composition of the outer planets C. based on consideration of the conditions that prevail where comets are located