You can tell the age of a tree by counting its ring. But these records of a tree’s life really say a lot more. Scientists are using tree ring to learn what’s been happening on the sun’s surface for the last ten thousand years. Each ring represents a year of growth. As the tree grows, it adds.a layer to its trunk, taking up chemical elements from the air. By looking at elements in the rings from a certain years, scientists can tell what elements were in the air that year. Dr. Stevenson is analyzing one element, carbon-d, in ring from both living and dead tree. Some ring go back almost ten thousand year to the end of the Ice Age. When Stevenson followed the carbon-14 levels changed with the intensity of solar burning. You see, the sun has cycles. Sometimes it burns fiercely, and at other times it is relatively calm. During the sun’s violent periods, it throw off charged particles in fast moving streams called "solar winds". The particularly interfere with the formation of carbon14 on earth. When there is more solar wind activity, less carbon-14 is produced. Ten thousand years of tree ring show that the carbon-14 level rises and falls about every 420 years. The scientists concluded that solar wind activity must follow the same cycle.
The purpose of the scientists in studying tree ring is to______.

A:examine the chemical elements in Ice Age B:look into the pattern of solar wind activity C:analyze the composition of different trees D:find out the origin of carbon-14 on earth

During its formative years, the inner solar system was a rough-and-tumble place. There were a couple of hundred large objects flying around. Moon-size or bigger, and for millions of years they collided with one another. Out of these impacts grew the terrestrial planets—Mercury, Venus, Earth with its Moon, and Mars—and the asteroids.
Scientists have thought of these collisions as mergers: a smaller object (the impactor) hits a larger one (the target) and sticks to it. But new computer modeling by Erik Asphaug and Craig B. Agnor of the University of California, Santa Cruz, shows that things weren’t that simple. "Most of the time, the impactor and the target go off on their merry ways," Dr. Asphaug said. About half the collisions are these hit-and-nm affairs. Now the two researchers and a colleague, Quentin Williams. have done simulations to study the effects of these collisions on the impactors. They are not pretty.
"The impactors suffer all kinds of fates," Dr. Asphaug said. They undergo tremendous shearing and gravitational forces that can cause them to fracture into smaller pieces or melt, causing chemical changes in the material and loss of water or other volatile compounds. Or the crust and cover can be stripped off. leaving just an embryonic iron core.
The researchers, whose findings are published in Nature, discovered that two objects did not even have to collide to create an effect on the smaller one. from the gravitational forces of a near-collision. During the simulations. Dr. Asphaug said, "We’d look and say, ’Gosh, we just got rid of the whole atmosphere of that planetoid: it didn’t even hit and it sucked the whole atmosphere off.’"
The researchers suggest that the remains of these beaten-up, fractured and melted objects can be found in the asteroid belt. Dr. Asphaug said that could explain the prevalence of "iron relics" in the belt. Some of these planetoid remnants also eventually hit Earth: that would help explain why certain meteorites lack water and other volatile elements.
The hit-and-run collision model also provides an explanation for Vesta. a large asteroid with an intact crust and cover. How did Vesta keep its cover while so many other objects were losing theirs Dr. Asphang said it could be that Vesta was always the target, never the impactor, and was thus less affected. "It just had to avoid being the hitter," he said, "until bigger objects left the system.

Certain meteorites lack water and other volatile elements probably because（）

A:these elements are not suitable to exist in these meteorites B:these elements are lost during the medical changes during collision C:their crest and cover have been stripped off D:they are planetoid remnants

During its formative years, the inner solar system was a rough-and-tumble place. There were a couple of hundred large objects flying around. Moon-size or bigger, and for millions of years they collided with one another. Out of these impacts grew the terrestrial planets—Mercury, Venus, Earth with its Moon, and Mars—and the asteroids.
Scientists have thought of these collisions as mergers: a smaller object (the impactor) hits a larger one (the target) and sticks to it. But new computer modeling by Erik Asphaug and Craig B. Agnor of the University of California, Santa Cruz, shows that things weren’t that simple. "Most of the time, the impactor and the target go off on their merry ways," Dr. Asphaug said. About half the collisions are these hit-and-nm affairs. Now the two researchers and a colleague, Quentin Williams. have done simulations to study the effects of these collisions on the impactors. They are not pretty.
"The impactors suffer all kinds of fates," Dr. Asphaug said. They undergo tremendous shearing and gravitational forces that can cause them to fracture into smaller pieces or melt, causing chemical changes in the material and loss of water or other volatile compounds. Or the crust and cover can be stripped off. leaving just an embryonic iron core.
The researchers, whose findings are published in Nature, discovered that two objects did not even have to collide to create an effect on the smaller one. from the gravitational forces of a near-collision. During the simulations. Dr. Asphaug said, "We’d look and say, ’Gosh, we just got rid of the whole atmosphere of that planetoid: it didn’t even hit and it sucked the whole atmosphere off.’"
The researchers suggest that the remains of these beaten-up, fractured and melted objects can be found in the asteroid belt. Dr. Asphaug said that could explain the prevalence of "iron relics" in the belt. Some of these planetoid remnants also eventually hit Earth: that would help explain why certain meteorites lack water and other volatile elements.
The hit-and-run collision model also provides an explanation for Vesta. a large asteroid with an intact crust and cover. How did Vesta keep its cover while so many other objects were losing theirs Dr. Asphang said it could be that Vesta was always the target, never the impactor, and was thus less affected. "It just had to avoid being the hitter," he said, "until bigger objects left the system./
Certain meteorites lack water and other volatile elements probably because______.

A:these elements are not suitable to exist in these meteorites B:these elements are lost during the medical changes during collision C:their crest and cover have been stripped off D:they are planetoid remnants

During its formative years, the inner solar system was a rough-and-tumble place. There were a couple of hundred large objects flying around. Moon-size or bigger, and for millions of years they collided with one another. Out of these impacts grew the terrestrial planets—Mercury, Venus, Earth with its Moon, and Mars—and the asteroids.
Scientists have thought of these collisions as mergers: a smaller object (the impactor) hits a larger one (the target) and sticks to it. But new computer modeling by Erik Asphaug and Craig B. Agnor of the University of California, Santa Cruz, shows that things weren’t that simple. "Most of the time, the impactor and the target go off on their merry ways," Dr. Asphaug said. About half the collisions are these hit-and-nm affairs. Now the two researchers and a colleague, Quentin Williams. have done simulations to study the effects of these collisions on the impactors. They are not pretty.
"The impactors suffer all kinds of fates," Dr. Asphaug said. They undergo tremendous shearing and gravitational forces that can cause them to fracture into smaller pieces or melt, causing chemical changes in the material and loss of water or other volatile compounds. Or the crust and cover can be stripped off. leaving just an embryonic iron core.
The researchers, whose findings are published in Nature, discovered that two objects did not even have to collide to create an effect on the smaller one. from the gravitational forces of a near-collision. During the simulations. Dr. Asphaug said, "We’d look and say, ’Gosh, we just got rid of the whole atmosphere of that planetoid: it didn’t even hit and it sucked the whole atmosphere off.’"
The researchers suggest that the remains of these beaten-up, fractured and melted objects can be found in the asteroid belt. Dr. Asphaug said that could explain the prevalence of "iron relics" in the belt. Some of these planetoid remnants also eventually hit Earth: that would help explain why certain meteorites lack water and other volatile elements.
The hit-and-run collision model also provides an explanation for Vesta. a large asteroid with an intact crust and cover. How did Vesta keep its cover while so many other objects were losing theirs Dr. Asphang said it could be that Vesta was always the target, never the impactor, and was thus less affected. "It just had to avoid being the hitter," he said, "until bigger objects left the system."

Certain meteorites lack water and other volatile elements probably because（）

A:these elements are not suitable to exist in these meteorites B:these elements are lost during the medical changes during collision C:their crest and cover have been stripped off D:they are planetoid remnants

{{B}}第二篇{{/B}}

The cause for the heat in the interior of the earth is______.

A:radioactive elements B:the great pressure of the earth C:not determined D:the heat remaining from the formation of the earth

{{B}}第二篇{{/B}}

The best title for the passage is ______.

A:The Heat Inside the Earth B:Volcanoes C:Radioactive Elements D:The Melted Rock

A schedule is commonly used in project planning and project portfolio management.（）on a schedule may be closely related to thework breakdown structure (WBS) terminal elements, the statement of work, or a contract data requirements list.

A:Essences B:Elements C:Purposes D:Issues

Software architecture reconstruction is an interpretive, interactive, and iterative process including many activities. (1) involves analyzing a system's existing design and implementation artifacts to construct a model of it. The result is used in the following activities to construct a view of the system. The database construction activity converts the (2) contained in the view into a standard format for storage in a database. The (3) activity involves defining and manipulating the information stored in database to reconcile, augment, and establish connections between the elements. Reconstruction consists of two primary activities: (4) and (5). The former provides a mechanism for the user to manipulate architectural elements, and the latter provides facilities for architecture reconstruction.

空白（2）处应选择（）

A:actors and usecases B:processes and data C:elements and relations D:schemas and tables

You can tell the age of a tree by counting its ring. But these records of a tree’s life really say a lot more. Scientists are using tree ring to learn what’s been happening on the sun’s surface for the last ten thousand years. Each ring represents a year of growth. As the tree grows, it adds a layer to its trunk, taking up chemical elements from the air. By looking at elements in the rings from a certain years, scientists can tell what elements were in the air that year. Dr. Stevenson is analyzing one element, carbon-14, in ring from both living and dead tree. Some ring go back almost ten thousand year to the end of the Ice Age. When Stevenson followed the carbon-14 levels changed with the intensity of solar burning. You see, the sun has cycles. Sometimes it bums fiercely, and at other times it is relatively calm. During the sun’s violent periods, it throw off charged particles in fast moving streams called "solar winds". The particularly interfere with the formation of carbon-14 on earth. When there is more solar wind activity, less carbon-14 is produced. Ten thousand years of tree ring show that the carbon-14 level rises and falls about every 420 years. The scientists concluded that solar wind activity must follow the same cycle.

The purpose of the scientists in studying tree ring is to （　）.

A:examine the chemical elements in Ice Age B:look into the pattern of solar wind activity C:analyze the composition of different trees D:find out the origin of carbon-14 on earth