A blue hole is a special kind of underwater cave found inland or in the sea, which forms when the earth above a cave falls in and water fills the space.
An inland blue hole’s water is very still and has different layers. A layer of fresh rainwater floats on top of salt water; the fresh water keeps oxygen from the atmosphere from reaching the salt water; brightly colored bacteria live where the two layers meet.
Diving into blue holes is extremely dangerous. Near the top of the blue hole, there is a layer of toxic gas, which causes itching, dizziness, and—in large amounts—death. Divers must also be fast. They have to get in and out of a cave before their oxygen runs out. Additionally, divers have to follow a guideline as they swim through a blue hole because it is very dark inside. Without the guideline, they may get lost.
If blue holes are so dangerous, why do explorers and scientists risk their lives to explore them? The reason is that these underwater caves can provide valuable scientific information. They provide clues about geology, archaeology, and biology. For example, some blue hole creatures, such as the remipede, probably haven’t changed for millions of years.
The blue holes could even provide clues about astrobiology. For example, divers have found bacteria there that can live without oxygen. Astrobiologist Kevin Hand says the bacteria may be similar to forms of life that might exist on Jupiter’s fourth largest moon, Europa. “Our study of life’s extremes on Earth,” he says, can help increase “our understanding of habitable environments off Earth.”
In addition, the oxygen-free environment of the blue holes preserves bones of humans and animals that fell into the caves long ago. By studying blue holes, we can understand what life was like in prehistoric times. As cave diver Kenny Broad says, “I can think of no other environment on Earth that is so challenging to explore and gives us back so much scientifically.”
24. What’s the main idea of Paragraph 1?
A. The structure of a blue hole. B. The location of a blue hole.
C. The formation of a blue hole. D. The definition of a blue hole.
25. Where can bright-colored bacteria be found?
A. In the saltwater layer. B. In the freshwater layer.
C. In between the freshwater and saltwater layers. D. In both of the freshwater and saltwater layers.
26. Which of the following best explains the underlined word?
A. The study of life on Earth. B. The study of life in the universe.
C. The study of life in prehistoric times. D. The study of life in oxygen-free environment.
27. Which of the following can best describe blue holes?
A. They’re oxygen-free and lifeless. B. They’re poisonous and dark.
C. They’re death zones and mazelike. D. They’re free of air and light.
24. D 25. C 26. B 27. B
这是一篇说明文。文章主要介绍了“蓝洞”这一事物，蓝洞是在内陆或海里发现的一种特殊的水下洞穴，它是当洞穴上方的地面塌陷，水充满空间时形成的。介绍了蓝洞的一些特性和重要意义。通过研究蓝洞，我们可以了解史前时代的生命是什么样子的。
24. D。主旨大意题。根据第一段可知，第一段的主旨是蓝洞的定义。
25. C。细节理解题。根据第二段第二句可知，在淡水和咸水层之间可以找到颜色鲜艳的细菌。
26. B。词句猜测题。根据画线词后文“For example, divers have found bacteria there that can live without oxygen以及“Our study of life’s extremes on Earth,” he says, can help increase “our understanding of habitable environments off Earth.”可知，蓝洞甚至可以提供有关宇宙生命的研究的线索。故画线词意思是“宇宙生命的研究”。
27. B。细节理解题。根据第三段前三句可知：潜入蓝洞是极其危险的。在蓝洞的顶部附近，有一层有毒气体，会导致瘙痒、头晕，量足够大人会死亡。潜水员还必须动作迅速。它们必须在氧气耗尽之前进出洞穴。 此外，潜水员在穿过蓝洞时必须遵循指南，因为洞内非常黑暗。换言之，蓝洞有毒且黑暗。
An inland blue hole’s water is very still and has different layers. A layer of fresh rainwater floats on top of salt water; the fresh water keeps oxygen from the atmosphere from reaching the salt water; brightly colored bacteria live where the two layers meet.
Diving into blue holes is extremely dangerous. Near the top of the blue hole, there is a layer of toxic gas, which causes itching, dizziness, and—in large amounts—death. Divers must also be fast. They have to get in and out of a cave before their oxygen runs out. Additionally, divers have to follow a guideline as they swim through a blue hole because it is very dark inside. Without the guideline, they may get lost.
If blue holes are so dangerous, why do explorers and scientists risk their lives to explore them? The reason is that these underwater caves can provide valuable scientific information. They provide clues about geology, archaeology, and biology. For example, some blue hole creatures, such as the remipede, probably haven’t changed for millions of years.
The blue holes could even provide clues about astrobiology. For example, divers have found bacteria there that can live without oxygen. Astrobiologist Kevin Hand says the bacteria may be similar to forms of life that might exist on Jupiter’s fourth largest moon, Europa. “Our study of life’s extremes on Earth,” he says, can help increase “our understanding of habitable environments off Earth.”
In addition, the oxygen-free environment of the blue holes preserves bones of humans and animals that fell into the caves long ago. By studying blue holes, we can understand what life was like in prehistoric times. As cave diver Kenny Broad says, “I can think of no other environment on Earth that is so challenging to explore and gives us back so much scientifically.”
24. What’s the main idea of Paragraph 1?
A. The structure of a blue hole. B. The location of a blue hole.
C. The formation of a blue hole. D. The definition of a blue hole.
25. Where can bright-colored bacteria be found?
A. In the saltwater layer. B. In the freshwater layer.
C. In between the freshwater and saltwater layers. D. In both of the freshwater and saltwater layers.
26. Which of the following best explains the underlined word?
A. The study of life on Earth. B. The study of life in the universe.
C. The study of life in prehistoric times. D. The study of life in oxygen-free environment.
27. Which of the following can best describe blue holes?
A. They’re oxygen-free and lifeless. B. They’re poisonous and dark.
C. They’re death zones and mazelike. D. They’re free of air and light.
24. D 25. C 26. B 27. B
这是一篇说明文。文章主要介绍了“蓝洞”这一事物，蓝洞是在内陆或海里发现的一种特殊的水下洞穴，它是当洞穴上方的地面塌陷，水充满空间时形成的。介绍了蓝洞的一些特性和重要意义。通过研究蓝洞，我们可以了解史前时代的生命是什么样子的。
24. D。主旨大意题。根据第一段可知，第一段的主旨是蓝洞的定义。
25. C。细节理解题。根据第二段第二句可知，在淡水和咸水层之间可以找到颜色鲜艳的细菌。
26. B。词句猜测题。根据画线词后文“For example, divers have found bacteria there that can live without oxygen以及“Our study of life’s extremes on Earth,” he says, can help increase “our understanding of habitable environments off Earth.”可知，蓝洞甚至可以提供有关宇宙生命的研究的线索。故画线词意思是“宇宙生命的研究”。
27. B。细节理解题。根据第三段前三句可知：潜入蓝洞是极其危险的。在蓝洞的顶部附近，有一层有毒气体，会导致瘙痒、头晕，量足够大人会死亡。潜水员还必须动作迅速。它们必须在氧气耗尽之前进出洞穴。 此外，潜水员在穿过蓝洞时必须遵循指南，因为洞内非常黑暗。换言之，蓝洞有毒且黑暗。
