Black Holes
1. Black holes can be best described as a sort of vacuum, sucking up everything in space. Scientists have discovered that black holes come from an explosion of huge stars. Stars that are near death can no longer burn due to loss of fuel, and because its temperature can no longer control the gravitational (重力的) force, hydrogen ends up putting pressure onto the star’s surface until it suddenly explodes then collapses.
2. Black holes come from stars that are made of hydrogen, other gases and a few metals. When these explode it can turn into a stellar-mass (恒星质量) black hole, which can only occur if the star is large enough (should be bigger than the sun) for the explosion to break it into pieces, and the gravity starts to compact every piece into the tiniest particle. Try to see and compare: if a star that’s ten times the size of the sun ends up being a black hole that’s no longer than 70 kilometers, then the Earth would become a black hole that’s only a fraction of an inch!
3. Objects that get sucked in a black hole will always remain there, never to break free. But remember that black holes can only gobble up (吞噬) objects within a specific distance to it. It’s possible for a large star near the sun to become a black hole, but the sun will continue to stay in place. Orbits do not change because the newly formed black hole contains exactly the same amount of mass as when it was a star, only this time its mass is totally contracted that it can end up as no bigger than a state.
4. So far, astronomers have figured out that black holes exist because of Albert Einstein’s theory of relativity. In the end, through numerous studies, they have discovered that black holes truly exist. Since black holes trap light and do not give off light, it is nearly impossible to detect black holes via a telescope. But astronomers continue to study galaxies, space and the solar system to understand how black holes might evolve. It is possible that black holes can exist for millions of years, and later contribute to a bigger process in galaxies, which can eventually lead to creation of new entities. Scientists also credit black holes as helpful in learning how galaxies began to form.
A. Is there proof that black holes really exist
B. What are different types of black holes
C. How are black holes formed
D. How were black holes named
E. What happens to the objects around a black hole
F. What are black holes made of
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The Tough Grass that Sweetens Our Lives
Sugar cane was once a wild grass that grew in New Guinea and was used by local people for roofing their houses and fencing their gardens. Gradually a different variety evolved which contained sucrose and was chewed on for its sweet taste. Over time, sugar cane became a highly valuable commercial plant, grown throughout the world. 46 Sugar became a vital ingredient in all kinds of things, from confectionery to medicine, and, as the demand for sugar grew, the industry became larger and more profitable. 47 Many crops withered and died, despite growers’ attempts to save them, and there were fears that the health of the plant would continue to deteriorate. In the 1960s, scientists working in Barbados looked for ways to make the commercial species stronger and more able to resist disease. They experimented with breeding programmes, mixing genes from the wild species of sugar cane, which tends to be tougher, with genes from the more delicate, commercial type. 48 This sugar cane is not yet ready to be sold commercially, but when this happens, it is expected to be incredibly profitable for the industry. 49 Brazil, which produces one quarter of the world’s sugar, has coordinated an international project under Professor Paulo Arrudo of the Universidade Estaudual de Campinas in Sao Paulo. Teams of experts have worked with him to discover more about which parts of the genetic structure of the plant are important for the production of sugar and its overall health. Despite all the research, however, we still do not fully understand how the genes function in sugar cane. 50 This gene is particularly exciting because it makes the plant resistant to rust, a disease which probably originated in India, but is now capable of infecting sugar cane across the world. Scientists believe they will eventually be able to grow a plant which cannot be destroyed by rust.
A.the 1980s,scientists have been analysing the mysterious of the sugar canes genetic code.
B.Unfortunately,however,the plant started to become weaker and more prone to disease.
C.The majority of the world’s sugar now comes from this particular commercial species.
D.One major gene has been identified by Dr. Angellique D’Hont and her team in Montpeller,France.
E.Eventually,a commercial plant was developed which was 5 percent sweeter than before,but also much stronger and less likely to die from disease.
F.Sugar cane is now much more vigorous and the supply of sugar is therefore more guaranteed.
He paused, waiting for her to digest the information.()
A.understand
B.withhold
C.exchange
D.contact
The contract between the two companies will expire soon.()
A.shorten
B.start
C.end
D.resume
Come out, or I’ll bust the door down.()
A.shut
B.break
C.set
D.beat
Make sure the table is securely anchored.()
A.repaired
B.cleared
C.booked
D.fixed
The police will need to keep a wary eye on this area of town.()
A.cautious
B.naked
C.blind
D.private
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