CIf a diver surfaces too quickly, he may suffer the bends.Nitrogen(氮) dissolved(溶解) in his blood is suddenly liberated by the reduction of pressure. The consequence, if the bubbles (气泡)accumulate in a joint, is sharp pain and abent body—thus the name.If the bubbles form in his lungs or his brain, the consequence can be death. Other air-breathing animals also suffer this decompression(减压) sickness if they surface too fast: whales, for example. And so, long ago, did ichthyosaurs. That these ancient sea animals got the bends can be seen from their bones. If bubbles of nitrogen form inside the bone they can cut off its blood supply. This kills the cells in the bone, and consequently weakens it, sometimes to the point of collapse. Fossil (化石)bones that have caved in on them selves are thus a sign that the animal once had the bends. Bruce Rothschild of the University of Kansas knewall this when he began a study of ichthyosaur bones to find out how widespread the problem was in the past. What he particularly wanted to investigate was how ichthyosaurs adapted to the problem of decompression over the 150 million years. To this end, he and his colleagues traveled the world’s natural-history museums, looking at hundreds of ichthyosaurs from the Triassic period and from the later Jurassic and Cretaceous periods. 　　When he started, he assumed that signs of the bends would be rarer in younger fossils, reflecting their gradual evolution of measures to deal with decompression. Instead, he was astonished to discover the opposite. More than 15% of Jurassic and Cretaceous ichthyosaurs had suffered the bends before they died, but not a single Triassic specimen(标本) showed evidence of that sort of injury. If ichthyosaurs did evolve an anti-decompression means, they clearly did so quickly—and, most strangely, they lost it afterwards. But that is not what Dr Rothschild thinks happened. He suspects it was evolution in other animals that caused the change. Whales that suffer the bends often do so because they have surfaced to escape a predator (捕食动物) such as a large shark. One of the features of Jurassic oceans was an abundance of large sharks and crocodiles, both of which were fond of ichthyosaur lunches. Triassic oceans, by contrast, were mercifully shark- and crocodile-free. In the Triassic, then, ichthyosaurs were top of the food chain. In the Jurassic and Cretaceous, they were prey(猎物) as well as predator—and often had to make a speedy exit as a result. The purpose of Rothschild’s study is to see（）

A:how often ichthyosaurs caught the bends B:how ichthyosaurs adapted to decompression C:why ichthyosaurs bent their bodies D:when ichthyosaurs broke their bones

CIf a diver surfaces too quickly, he may suffer the bends.Nitrogen(氮) dissolved(溶解) in his blood is suddenly liberated by the reduction of pressure. The consequence, if the bubbles (气泡)accumulate in a joint, is sharp pain and abent body—thus the name.If the bubbles form in his lungs or his brain, the consequence can be death. Other air-breathing animals also suffer this decompression(减压) sickness if they surface too fast: whales, for example. And so, long ago, did ichthyosaurs. That these ancient sea animals got the bends can be seen from their bones. If bubbles of nitrogen form inside the bone they can cut off its blood supply. This kills the cells in the bone, and consequently weakens it, sometimes to the point of collapse. Fossil (化石)bones that have caved in on them selves are thus a sign that the animal once had the bends. Bruce Rothschild of the University of Kansas knewall this when he began a study of ichthyosaur bones to find out how widespread the problem was in the past. What he particularly wanted to investigate was how ichthyosaurs adapted to the problem of decompression over the 150 million years. To this end, he and his colleagues traveled the world’s natural-history museums, looking at hundreds of ichthyosaurs from the Triassic period and from the later Jurassic and Cretaceous periods. 　　When he started, he assumed that signs of the bends would be rarer in younger fossils, reflecting their gradual evolution of measures to deal with decompression. Instead, he was astonished to discover the opposite. More than 15% of Jurassic and Cretaceous ichthyosaurs had suffered the bends before they died, but not a single Triassic specimen(标本) showed evidence of that sort of injury. If ichthyosaurs did evolve an anti-decompression means, they clearly did so quickly—and, most strangely, they lost it afterwards. But that is not what Dr Rothschild thinks happened. He suspects it was evolution in other animals that caused the change. Whales that suffer the bends often do so because they have surfaced to escape a predator (捕食动物) such as a large shark. One of the features of Jurassic oceans was an abundance of large sharks and crocodiles, both of which were fond of ichthyosaur lunches. Triassic oceans, by contrast, were mercifully shark- and crocodile-free. In the Triassic, then, ichthyosaurs were top of the food chain. In the Jurassic and Cretaceous, they were prey(猎物) as well as predator—and often had to make a speedy exit as a result. Rothschild might have concluded that ichthyosaurs（）

A:failed to evolve an anti decompression means B:gradually developed measures against the bends C:died out because of large sharks and crocodiles D:evolved an anti decompression means but soon lost it

The river widens considerably as it begins to turn west.

A:extends B:stretches C:broadens D:bends

Scientists can’t yet make an invisibility cloak like the one that Harry Potter uses. But, for the first time, they’ve constructed a simple cloaking device that makes itself and something placed inside it invisible to microwaves.
When a person "sees" an object, his or her eye senses many different waves of visible light as they bounce off the object. The eye and brain then work together to organize the sesensations and reconstruct the object’s original shape. So, to make an object invisible, scientists have to keep waves from bouncing off it. And they have to make sure the object casts no shadow. Otherwise, the absence of reflected light on one side would give the object away.
Invisibility isn’t possible yet with waves of light that the human eye can see. But it is now possible with microwaves. Like visible light, microwaves are a form of radiant energy. They are part of the electromagnetic spectrum, which also includes radio waves, infrared light, ultraviolet rays, X rays, and gamma rays. The wave lengths of microwaves are shorter than those of radio waves but longer than those of visible light.
The scientists’ new "invisibility device" is the size of a drink coaster and shaped like a ring. The ring is made of a special material with unusual ability. When microwaves strike the ring, very few bounce off it. Instead, they pass through the ring, which bends the waves all the way around until they reach the opposite side. The waves then return to their original paths.
To a detector set up to receive microwaves on the other side of the ring, it looks as if the waves never changed their paths as if there were no object in the way! So, the ring is effectively invisible.
When the researchers put a small copper loop inside the ring, it, too, is nearly invisible. However, the cloaking device and anything inside it do cast a pale shadow. And the device works only for microwaves, not for visible light or any kind of electromagnetic radiation. So, Harry Potter’s invisibility cloak doesn’t have any real competition yet.
What is NOT true of the invisibility device

A:It is made of a special material with unusual ability. B:Microwaves bounce off it when they strike it. C:Microwaves pass through it when they strike it. D:It bends the microwaves all the way around until they reach the opposite sid

下面有3篇短文，每篇短文后有5道题，每题后面有4个选项。请仔细阅读短文并根据短文回答其后面的问题，从4个选项中选择1个最佳答案。
{{B}}第一篇{{/B}}

What is NOT true of the invisibility device?

A:It is made of a special material with unusual ability. B:Microwaves bounce off it when they strike it. C:Microwaves pass through it when they strike it. D:It bends the microwaves all the way around until they reach the opposite side.

The river{{U}} widens{{/U}} considerably as it begins to turn west

A:extends B:stretches C:broadens D:bends