Question

根據(jù)短文內(nèi)容，從下邊的A—F選項中選出能概括每一段主題的最佳選項。選項中有一項為多余選項。

A . The different structure of blue holes.????????

B. Why scientists are interested in blue holes.????????

C. How a blue hole comes into being.

D. Blue holes exploring is becoming popular.

E. Rules to obey when diving into blue holes.

F. The general definition of a blue hole.

1.______________

??? A blue hole is a flooded sea cave with a hole that opens up at the land's surface. These cave systems form in carbonate rock, often on islands. Some blue holes have very special rock formations and water chemistry. Far below sea level, they contain some of the harshest environments on Earth, with no oxygen and no light. Yet these areas are filled with life forms that have adapted to the extreme conditions.

2.___________

??? Blue holes get their name from the color some have when seen from the air. The color is usually a reflection of the sky on the water. Blue holes are the result of erosion in which water breaks down rock. Rain falling thousands of years ago contained chemicals which slowly wore away at the limestone landmass. These holes later filled with sea water as the sea level changed. The rising and falling of sea levels and the mixture of salt and fresh water further wore away at these cave formations.

3. ____________

??? These flooded cave systems can be found in the ocean, or they can be found inland. Ocean caves are affected by tides, so they always have water movement. But blue holes on land are very still. They have several layers of water, chemicals, and bacteria. The top layer of fresh water comes from rainfall. This layer acts like a cap on top of the layered mixture, and keeps out oxygen from the atmosphere. The fresh water floats on a denser layer of saltwater. Underneath this is a layer of poisonous hydrogen sulfide, produced by bacteria living in the water. Underneath this layer is anoxic seawater -- water that does not contain any oxygen.

4.___________

??? Information gathered from these blue holes is helping scientists to increase their understanding of biology, archaeology and geology. But exploring these blue hole environments brings danger as well as discovery. Scientists are interested in these caves because oxygen-free conditions there are similar to those on Earth long ago, before oxygen existed on our planet. But there are many difficulties involved in diving into blue holes.

5.___________

One reason blue holes have not been fully explored is that they can be extremely dangerous. There are many safety rules that divers must follow to help ensure their survival. First, divers must have training and experience to swim in these caves. Divers who explore a cave for the first time must establish a thin rope called a guideline. This line helps them to safely enter and exit the cave without getting lost.

 

Answer 1

【答案】

1.F

2.C

3.A

4.B

5.E

【解析】

試題分析：本文主要講述的是blue hole如何形成，具體結(jié)構(gòu)以及科學(xué)家對它產(chǎn)生興趣的原因，最后還提及了人們在研究它的時候所要遵循的基本規(guī)則。

1.F 根據(jù)本段第一句A blue hole is a flooded sea cave with a hole that opens up at the land's surface.可知本段主要介紹的是什么是blue hole，也就是blue hole的定義。故F正確。

2.C 根據(jù)本段2,3,4行Blue holes are the result of erosion in which water breaks down rock. Rain falling thousands of years ago contained chemicals which slowly wore away at the limestone landmass. These holes later filled with sea water as the sea level changed.可知本段主要講述的是blue hole是如何形成的，也就是分析它產(chǎn)生的原因。故Ｃ項正確。

3.A 根據(jù)本段2,3,4,5行They have several layers of water, chemicals, and bacteria. The top layer of fresh water comes from rainfall. This layer acts like a cap on top of the layered mixture, and keeps out oxygen from the atmosphere. The fresh water floats on a denser layer of saltwater. Underneath this is a layer of poisonous hydrogen sulfide, produced by bacteria living in the water.可知主要講述的blue hole的構(gòu)造和不同的結(jié)構(gòu)中的具體的組成。故A項正確。

4.B 根據(jù)本段3,4行Scientists are interested in these caves because oxygen-free conditions there are similar to those on Earth long ago, before oxygen existed on our planet.可知本段主要解釋科學(xué)家對于blue hole感興趣的原因。故B正確。

5.E 根據(jù)本段第2句There are many safety rules that divers must follow to help ensure their survival.可知本段主要講述的是在探索blue hole的時候要遵循的安全規(guī)則。故E項正確。

考點：考察科普類短文閱讀