2014年6月21日托福阅读真题P3+题目+答案：The Origin of Coral Reefs

2014年6月21日托福阅读真题P3+题目+答案：The Origin of Coral Reefs

Coral reefs are natural structures formed from deposits of the calcium carbonate secretions of coral, a marine animal that lives in colonies. In general, coral reefs are grouped into one of three categories, atolls, barrier reefs, and fringing reefs. Atolls are usually easily distinguished because they are modified horseshoe-shaped reefs that rise out of very deep water far from land and enclose a lagoon (a body of certain water surrounded by a coral reef). With few exceptions, atolls are found only in the Indo-Pacific area. Barrier reefs and fringing reefs, on the other hand, tend to grade into each other and are not readily separable. Some scientists would prefer to group them into a single category. Both types occur adjacent to a landmass, with a barrier reef being separated from the landmass by a greater distance and deeper water channel than the fringing reef. Fringing reefs and barrier reefs are common throughout the coral reef zones in all oceans。

1. According to paragraph 1, all of the following are true of atolls EXCEPT

A.Most atolls occur in the Indo-Pacific area.

B.Atolls occur only in very deep waters.

C.Atolls are more common than other types of reefs.

D.Atolls occur far from a landmass.

2. According to paragraph 1, fringing reefs and barrier reefs can be identified by

A.their similarities to atolls

B.their organization into groups of separable parts

C.their distance from the nearest landmass

D.whether or not they enclose a lagoon

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——the ………………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.

3. The phrase “was heightened” in the passage is closest in meaning to

A.developed

B.varied

C.continued

D.increased

4. The word “prevail” in the passage is closet in meaning to

A.dominate

B.combine

C.spread

D.compete

5. Which of the following can be inferred from paragraph 2 as the reason that the origin of atolls has generated more interest than has the origin of other types of reefs?

A.Most reefs have a predictable shape, but atolls do not.

B.Atolls appear to form more rapidly than other kinds of reefs.

C.The animals that form coral reefs cannot live in water below 70 meters, but atolls only form in very deep water.

D.Atolls have more diverse origins and histories than other types of reefs.

6. According to paragraph 2, Darwin’s subsidence theory provided an answer to each of the following questions EXCEPT

A.How does a lagoon develop?

B.Why do volcanic islands subside?

C.How does a fringing reef become a barrier reef?

D.What happens to coral growth when a volcanic island subsides slowly?

7. What can be inferred from paragraph 2 about the development of atolls according to Darwin’s theory?

A.All atolls begin as fringing reefs.

B.An atoll will not develop if an island subsides too slowly.

C.Most atolls will eventually become barrier reefs.

D.The formation of a lagoon accelerates the overall development of an atoll.

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