Question

根据短文内容，从下边的A—F选项中选出能概括每一段主题的最佳选项。选项中有一项为多余选项。
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.
小题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.
小题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.
小题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.
小题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.
小题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

小题1:F
小题2:C
小题3:A
小题4:B
小题5:E

试题分析：文章介绍了探索地球上神秘的蓝洞，包括蓝洞的定义，蓝洞是怎么形成的，蓝洞的不同的结构等。
小题1:考查段落大意和句意理解：根据这段的句子：A blue hole is a flooded sea cave with a hole that opens up at the land's surface.可知这段讲的是：蓝洞的大致的定义。答案是F
小题2:考查段落大意和句意理解：根据这段的句子：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.可知这段讲的是：蓝洞是怎么形成的，答案是C
小题3:考查段落大意和句意理解：根据这段的句子：They have several layers of water, chemicals, and bacteria.可知这段讲的是：蓝洞的不同的结构，答案是A
小题4:考查段落大意和句意理解：根据这段的句子：Scientists are interested in these caves because oxygen-free conditions there are similar to those on Earth long ago,可知这段讲的是：为什么科学家对蓝洞感兴趣，答案是B
小题5:考查段落大意和句意理解：根据这段的句子：There are many safety rules that divers must follow to help ensure their survival.可知这段讲的是：潜入蓝洞要注意的规定，答案是E