意为珊瑚礁从下沉的岛屿上长出来，然后变成裙礁，再变成堡礁，最后岛屿消失变成环礁，对应选项C中：Darwin … as a coral reef … a sinking island, … fringing reef, … barrier reef, and … disappearance of the island, an atoll.
9. Which of the following can be inferred from paragraph 3 about the Pacific atolls? 【推理题】
A. They were once fringing reefs around the coasts of islands.
B. They were first observed by Darwin during his voyage on the Beagle.
C. They will eventually become fringing reefs.
D. They are located where the ocean floor does not sink.
答案：A
解析：原文A long time after Darwin put forward this theory, some deep boreholes were drilled in the Pacific atolls in the 1950s. … and indicated that the coral … growing upward … as Earth's crust subsided .... Darwin s theory was therefore proved basically correct，说明太平洋环礁随着地球地壳减少慢慢上涨而形成的，证明达尔文理论正确，所以太平洋环礁最初就是围绕岛屿的裙礁，对应选项A中：They were once fringing reefs around the coasts of islands。
10. Why does the passage provide the information that the drill holes in the Pacific atolls passed through more than a thousand meters of coral before reaching the rock substratum of the ocean floor? 【组织结构题】
A. To emphasize that according to Darwin’s view coral can grow at great depths
B. To indicate how scientists knew the rate at which Earth’s crust had subsided
C. To support the claim that coral reefs take millions of years to form
D. To present the evidence that confirmed Darwin’s account of coral reef evolution
答案：D
解析：原文Darwin s theory was therefore proved basically correct，说明举例太平洋环礁就是为了证明达尔文理论正确，对应选项D中：To present the evidence that confirmed Darwin’s account of coral reef evolution。
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