TOEFL Reading: ETS-TOEFL阅读机经 - X4F35LOR30814373L$

Which of the following is mentioned in paragraph 3 as the reason many scientists doubted Darwin's theory of how atolls form? A. After Darwin's five-year voyage, different kinds of atolls than those he observed were discovered. B. Scientists discovered guyots, or flat-topped mountains, below the ocean's surface. C. Surface features of atolls do not show any signs of a volcanic base. D. Drilling through layers of atoll reef did not produce the results Darwin predicted.