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A black hole is created when a large star burns out. Like our sun, stars are unbelievably hot furnaces (熔炉) that burn their own matter as fuel. When most of the fuel is used up, the star begins to die.
The death of a star is not a quiet event. First there is a huge explosion. As its outer layer is blasted off into space, the dying star shines as brightly as a billion suns.
After the explosion gravity pulls in what’s left of the star. As the outside of the star sinks toward the center, the star gets smaller and smaller. The material the star is made of becomes tightly packed together. A star is so dense that a teaspoon of matter from it weighs billion of pounds.
The more the star shrinks, the stronger the gravity inside it becomes. Soon the star is very tiny, and the gravity pulling it in is unbelievably strong. In fact, the gravity is so strong that it even pulls light into the star! Since all the light is pulled in, none can go out. The star becomes black when there is no light. Then a black hole is born!
That’s what we know about black holes. What we don’t know is this: What happens inside a black hole after the star has been squeezed into a tiny ball? Does it keep getting smaller and smaller forever? Such a possibility is hard to imagine.
But if the black hole doesn’t keep shrinking, what happens to it? Some scientists think black holes are like doorways to another world. They say that as the star disappears from our universe, it goes into another universe. In other words a black hole in our universe could turn into a “white hole” in a different universe. As the black hole swallows light, the white hole shines brightly—somewhere else. But where? A different place, perhaps, or a different time — many years in the past or future.
Could you travel through a black hole? Right now, no. Nothing we know of could go into a black hole without being crushed. So far the time being, black hole must remain a mystery.
Black holes are a mystery—but that hasn’t stopped scientists from dreaming about them. One scientist suggested that in the future we might make use of the power of black holes. They would supply all of Earth’s energy needs, with plenty to spare. Another scientist wondered if a black hole could some day be used to swallow earthly waste—a sort of huge waste disposal(处理) in the sky!
When the star begins to die ______.
A. there is no fuel left in it B. its outer layer goes into space first
C. a huge explosion will happen D. it doesn’t give off light any longer
Which of the following doesn’t help produce a black hole?
A. The gravity inside the star is very strong. B. The light can’t go out of the star.
C. The star becomes smaller and smaller D. The dying star shines very brightly.
The black hole ______.
A. continues becoming smaller and smaller all the time
B. goes into another universe and becomes a white hole
C. can pull in everything we know of in the world
D. will appear at another place at a different time
What’s the best title for this passage?
A. A New Scientific Discovery: Black Holes
B. How Do Black Holes Come Into Being?
C. What Are Black Holes?
D. Travel Through A Black Hole
查看习题详情和答案>>A black hole is created when a large star burns out. Like our sun, stars are unbelievably hot furnaces(熔炉) that burn their own matter as fuel. When most of the fuel is used up, the star begins to die.
The death of a star is not a quiet event. First there is a huge explosion. As its outer layer is blasted off into space, the dying star shines as brightly as a billion suns.
After the explosion gravity pulls in what’s left of the star. As the outside of the star sinks toward the center, the star gets smaller and smaller. The material the star is made of becomes tightly packed together. A star is so dense that a teaspoon of matter from it weighs billion of pounds.
The more the star shrinks, the stronger the gravity inside it becomes. Soon the star is very tiny, and the gravity pulling it in is unbelievably strong. In fact, the gravity is so strong that it even pulls light into the star! Since all the light is pulled in, none can go out. The star becomes black when there is no light. Then a black hole is born!
That’s what we know about black holes. What we don’t know is this: What happens inside a black hole after the star has been squeezed into a tiny ball? Does it keep getting smaller and smaller forever? Such a possibility is hard to imagine.
But if the black hole doesn’t keep shrinking, what happens to it? Some scientists think black holes are like doorways to another world.They say that as the star disappears from our universe, it goes into another universe. In other words a black hole in our universe could turn into a “white hole” in a different universe. As the black hole swallows light, the white hole shines brightly — somewhere else. But where? A different place, perhaps, or a different time — many years in the past or future.
Could you travel through a black hole? Right now, no. Nothing we know of could go into a black hole without being crushed.So far the time being, black hole must remain a mystery.
Black holes are a mystery—but that hasn’t stopped scientists from dreaming about them. One scientist suggested that in the future we might make use of the power of black holes. They would supply all of Earth’s energy needs, with plenty to spare. Another scientist wondered if a black hole could some day be used to swallow earthly waste—a sort of huge waste disposal (处理) in the sky!
When the star begins to die ______.
A.there is no fuel left in it B.its outer layer goes into space first
C.a huge explosion will happen D.it doesn’t give off light any longer
Which of the following doesn’t help produce a black hole?
A.The gravity inside the star is very strong.
B.The light can’t go out of the star.
C.The star becomes smaller and smaller
D.The dying star shines very brightly.
The black hole ______.
A.continues becoming smaller and smaller all the time
B.goes into another universe and becomes a white hole
C.can pull in everything we know of in the world
D.will appear at another place at a different time
What’s the best title for this passage?
A.A New Scientific Discovery: Black Holes
B.How Do Black Holes Come Into Being?
C.What Are Black Holes?
D.Travel Through A Black Hole
查看习题详情和答案>>A little under one-third of U.S. families have no Internet access and do not plan to get it, with most of the holdouts seeing little use for it in their lives, according to a survey released on Friday.
Park Associates, a Dallas-based technology market research firm, said 29 percent of U.S. families, or 31 million homes, do not have Internet access and do not intend to subscribe(预订) to an Internet service over the next 12 months. The second annual National Technology Scan conducted by Park found that the main reason why potential customers say they do not subscribe to the Internet is because of the low value to their daily lives rather than concerns over cost.
Forty-four percent of these families say they are not interested in anything on the Internet, versus just 22 percent who say they cannot afford a computer or the cost of Internet service, the survey showed. The answer "I'm not sure how to use the Internet" came from 17 percent of participants who do not subscribe. The response "I do all my e-commerce shopping and YouTube-watching at work" was cited by 14 percent of Internet-access refuseniks. Three percent said the Internet doesn't reach their homes.
The study found U.S. broadband adoption grew to 52 percent over 2006, up from 42 percent in 2005. Roughly half of new subscribers converted(转变) from slower-speed, dial-up Internet access while the other half of families had no prior access.
"The industry continues to chip (击破)away at the core of non-subscribers, but has a long way to go," said John Barrett, director of research at Parks Associates. "Entertainment applications will be the key. If anything will pull in the holdouts, it's going to be applications that make the Internet more similar to pay-TV," he predicted.
What does the underlined word “holdouts” in the first paragraph most probably mean?
A. some American families
B. those who hold out one’s opinions
C. those who have been surveyed
D. those who still haven’t access to the Internet currently
Many potential customers refuse to subscribe to the Internet mainly because __________.
A. they show too much concern about the cost
B. they can find little value of it
C. they do most YouTube-watching at work
D. the Internet doesn’t reach their homes
From the passage we can infer that _____________.
A. It is not an easy job to transform those holdouts into the Internet users
B. people will adopt dial-up Internet access no more
C. many Americans enjoy doing e-commerce shopping at home
D. more than half of the population are using the Internet in 2005
According to John Barrett, what is the key to attracting more U.S. families to broadband service?
A. making the Internet look more similar to TV set
B. applying the Internet more to entertainment
C. providing more pay-TV programs
D. chipping away at the core of non-subscribers
Which is the best title for the passage?
A. Web develops with technology
B. The present situation of web
C. Many Americans see little point to web
D. It is urgent to promote web service
查看习题详情和答案>>A volcanic eruption in Iceland has sent ash across northern Europe. Airlines have stopped or changed the flights across the Atlantic Ocean, leaving hundreds of passengers stuck in airports.
Grirmsvom is one of the largest and most active volcanoes in Europe. What makes Grimsvom different is that it lies under a huge glacier(冰川) of ice up to 12 maters thick. The hot volcano heats up the ice above it, which then forms a layer(层)of water between the glacier and the volcano This layer of water puts pressure on the volcano, keeping it stable, As the water flows out from under the glacier, the pressure lifts. The lava(岩浆) from the volcano then comes up to the surface. This is exactly what happened today.
Now, airlines have to make changes to their flights so as not to fly through the clouds of volcanic ash. According to KLM. one of Europe’s biggest airlines, airplanes cannot go under the cloud or over it. Going through the cloud can result in ash getting stuck in the airplane’s engines, causing damage to the plane.
The eruption has also caused problems for animals in Iceland. The volcano left ash and sharp. Glass-like rocks all over the countryside. Farmers are keeping their animals inside to stop them from eating ash- covered grass to the sharp object.
What keeps Grimsvom still?
A. The slow flow of water B. The low water temperature
C. The thick glacier D. The water pressure
Which of the following is true?
A. People stop traveling in Europe
B. Airlines suffer from the loss of planes
C. It becomes dangerous for animals to eat outside
D. Farmers have lost many of their animals
This text is most probably taken from_______________.
A. a research paper B. a newspaper report
C. a class presentation D. a geography textbook.
查看习题详情和答案>>A simple piece of clothesline hangs between some environmentally friendly Americans and their neighbors.
On one side stand those who see clothes dryers(干衣机) as a waste of energy and a major polluter of the environment. As a result, they are turning to clotheslines as part of the “what-I –can do environmentalism(环境保护主义).”
On the other side are people who are against drying clothes outside, arguing that clotheslines are unpleasant to look at. They have persuaded Homeowners Associations (HOAs) access the U.S. to ban outdoor clotheslines, because clothesline drying also tends to lower home value in the neighborhood. This had led to a Right-to-Dry Movement that is calling for laws to be passed to protect people’s right to use clotheslines.
So far, only three states have laws to protect clothesline. Right-to-Dry supporters argue that there should be move.
Matt Reck, 37, is the kind of eco-conscious(有生态意识的) person who feeds his trees with bathwater and reuses water drops from his air conditioners to water plants. His family also uses a clothesline. But on July 9, 2007, the HOA in Wake Forest, North Carolina, told him that a dissatisfied neighlzir had telephoned them about him clothesline. The Recks paid no attention to the warming and still dried their clothes on a line in the yard. “Many people say they are environmentally friendly but they don’t take matters in their own hands,” says Reck. The local HOA has decided not to take any action, unless more neighbors come to them.
North Carolina lawmakers are saying that banning clotheslines is not the right thing to do. But HOAs and housing businesses believe that clothesline drying reminds people of poor neighborhoods. They worry that if buyers think their future neighbors can’t even afford dryers, housing prices will fall.
Environmentalists say such worries are not necessary, and in view of global warming, that idea needs to change. As they say, “The clothesline is beautiful”. Hanging clothes outside should be encouraged. We all have to do at least something to slow down the process of global warming.”
One of the reasons why supporters of clothes dryers are trying to ban clothesline drying is that ____.
A. clothes dryers are more efficient B. clothesline drying reduces home value
C. clothes dryers are energy-saving D. clothesline drying is not allowed in most U.S. states
Which of the following best describes Matt Reck?
A. He is a kind-hearted man. B. He is an impolite man.
C. He is and experienced gardener. D. He is a man of social responsibility.
Who are in favor of clothesline drying?
A. housing businesses. B. Environmentalists.
C. Homeowners Associations. D. Reck’s dissatisfied neighbors.
What is mainly discussed in the text?
A. Clothesline drying: a way to save energy and money.
B. Clothesline drying: a lost art rediscovered.
C. Opposite opinions on clothesline drying.
D. Different varieties of clotheslines.
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