Different types of reefs and reefs in different oceans may have diverse origins and histories. The greatest interest in the origin of reefs has centered on atolls. For many years, humans speculated as to how such reefs could develop in such deep water, miles from the nearest emergent land. This interest was heightened when it was discovered that reef corals cold not live deeper than 50-70 meters. This led to the development of several theories concerning the origin of atolls. Only one need be discussed here — Darwin’s subsidence theory —the fringe corals grow on the shores of newly formed volcanic islands that have pushed to the surface from deep water. These islands often begin to subside, and if the subsidence is not too fast, reef growth will keep up with the subsidence. The reef growth will then form a barrier reef and, ultimately, an atoll as the island disappears beneath the sea. When the island has disappeared, corals continue to grow on the outside and keep the reef at the surface. On the inside, where the island used to be, quiet water conditions and high sedimentation prevail. These conditions prevent continued vigorous coral growth, hence, a lagoon develops. This theory links all three reef types into evolutionary sequence, but is not an explanation for all fringing and barrier reef types.
1. 段落中心并非首句直接引出，前面都是铺垫，一直到 This led to the development of several theories，才明白，前面讲的都是为了引出理论！
What can be inferred from paragraph 2 about the development of atolls according to Darwin’s theory?
答案选的是：All atolls begin as fringing reefs.
很多同学看到这个选项就立刻排除了，说后面不是否定了达尔文理论吗，不是明显驳斥吗？殊不知，题目问的，就是 according to Darwin’s theory ，所以，哪怕达尔文理论不对，也得选这个理论呀！