题目内容
A team of international researchers has found new evidence that an endangered subspecies of chimpanzee is the source of the virus that causes acquired immune deficiency syndrome (AIDS) in humans. Experts said the finding could lead to new treatments for AIDS and contribute to the development of a vaccine against the disease.
The research team said the chimp -- a subspecies known as Pan troglodytes troglodytes native to west central Africa -- carries a simixan immunodeficiency virus (SIV) that is closely related to three strains of human immunodeficiency virus (HIV), the virus that causes AIDS. One of these strains, HIV - 1, has caused the vast majority of the estimated 30 million HIV infections around the world.
The researchers are uncertain When the chimp virus, called SIVcpz (for simixan immunodeficiency virus chimpanzee), first infected humans, although the oldest documented case of HIV has been linked to a Bantu man who died in Central Africa in 1959. But they said the virus, which does not appear to harm the chimps, was most likely transmixtted to humans when hunters were exposed to chimp blood while killing and butchering the animals for food. Once transmixtted to humans, the researchers believe the virus mutated into HIV - 1.
Team leader Beatrice Hahn, an AIDS researcher at the University of Alabama in Birmingham, said the chimps have probably carried the virus for hundreds of thousands of years. Since humans have likely hunted the animals since prehistoric times, Hahn said the virus may have jumped to humans on many occasions, but was not transmixtted widely among humans until the 20th century. Increased hunting of the chimpanzees, along with human mixgration to African cities and changing sexual mores, could help explain the recent epidemixc, Hahn said.
Scientists had long suspected that a nonhuman primate was the source of HIV - 1. Earlier studies suggested that the sooty mangabey monkey, a native of West Africa, was the likely source of HIV - 2 -- a rarer form. of the AIDS virus that is transmixtted less easily than HIV - 1. However, only a few samples of SIV strains exist, making it difficult for researchers to confidently connect the strains to HIV - 1.
As part of their effort to discover the source of HIV - 1, the research team studied the four known samples of SIVcpz. They learned that three of the four samples came from chimps belonging to the subspecies P.t. troglodytes. The remaining sample came from another subspecies, Pan troglodytes schweinfurthii, which inhabits East Africa.
The team then compared the SIVcpz strains to each other and found that all three of the viruses from P. t. troglodytes were closely related, while the virus from P.t. schweinfurthii was genetically different. Next they compared the SIVcpz strains to the main subgroups of HIV - 1, known as M, N, and O. Their comparisons showed that the P.t. troglodytes viruses strongly resembled all three HIV - 1 subgroups.
Additional evidence that HIV - 1 could be linked to P. t. troglodytes came when the researchers examined the chimps' natural habitat. The researchers quickly discovered that the chimps live primarily in the West African nations of Cameroon, Central African Republic, Gabon, Equatorial Guinea, and Republic of the Congo the geographic region where HIV -1 was first identified.
Upon closer study, the researchers learned that the chimps were being killed in growing numbers for the so - called bushmeat trade, a trend assisted by the construction of new logging roads in once remote forests. The researchers said that continued hunting of the animals meant that many people are still likely to be exposed to SIVcpz, increasing the risk of additional cross - species transmissions.
Many AIDS researchers welcomed the team's finding, but said the new work had not proved the connection definitively. Most of the doubts centered on the difficulty of drawing conc
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SECTION C NEWS BROADCAST
Directions: In this section you will hear everything ONCE ONLY. Listen carefully and then answer the questions that follow. At the end of each news item, you will be given 10 seconds to answer the questions.
听力原文： The first prototype of an aircraft intended to revolutionize travel and shatter speed records was destroyed during its maiden flight on Saturday after a booster rocket carrying it a- loft veered out of control and tumbled from the sky.
US space scientists were forced to destroy the un- manned X43A prototype in midair just minutes before the plane was due to fire the oxygen scooping "scramjet" engine designed to drive it at seven times the speed of sound.
NASA cameras aboard two F-18 chase planes showed the Pegasus rocket careening off course and failing out of control from the sky before controlers triggered on board explosures to destroy it over the Pacific Ocean at about 1:45 pm PDT (4:45 pm EDT/2045 GMT)
Pieces of the booster rocket and the small, black X- 43A prototype, part of NASA' s "Hyper-X" programme, fell into the sea.
What's happening？
After so many years of studying English, you may still get confused like you first come here just because of the slang the students use! Now let us see how "street talk" and "regional talk" are.
Street talk is a way to categorize many "hip" words used on the street. There is a playfulness about street talk.
What about the word "hip？" You might have thought that this was derived from "hippie"--a follower of social fashion in the 1960s and 70s. But no, it comes from a much older usage, the word “hep”. The word “hip” is marked as "out-of-date slang". But it seems to have come back into fashion.
Other bits of old-fashioned slang are also popular here, such as "cool'. The expression "that's cool" is often used to agree to a suggestion.
The problem with slang and trendy expressions in general is that they change fast, so that only those who are using them all the time can keep up.
A great deal of slang used by students comes from television and films,especially from "catch phrases" that are used by characters in TV programmes or films.
A "catchphrase" is a phrase that a particular character repeats. If you live here among students, go out to the cinema, watch similar programes and listen to popular music, you might find yourself using slang with- out even thinking.
If you meet students from outside London and the south-east, you may notice that local people some- times don't use textbook English.
Traditional dialects are dying out here. But there are still many regional variations in the way English is used.
One example is the way people address each other. If you are in Newcastle, you might hear people (particularly women) refer to each other as "hinny"--a common term of endearment. "Hinny" refers to the "sterile hybrid offspring of a male horse and female donkey," but that is not what they mean when they call you "hinny" in Newcastle ! Probably, the word they're using is the local form. of "honey".
Other parts have their own endearments. If someone in Glasgow calls you" hen" or someone in Nottingham adds "duck" to the end of what they say ,they're being friendly, not rude.
Younger people tend to use these terms less. And these phrases are only the tip of the iceberg when it comes to the rich regional variations found in informal speech here today.
So after you think you've got the hang of slang, do you dare use it yourself？ Take care! Most informal and colloquial usage marks you as coming from a particular social background--to a native speaking thing.
Since English is not your first language, people may find it odd if you use slang. But you should spare time for chatting with, and learning from native - speakers and try to understand different usages. As you gain experience, you'll learn which phrases are safe to use. But make sure you don't use them in the wrong place. Stick with official English whenever in doubt!
The author is a ______.
SECTION B INTERVIEW
Directions: In this section you will hear everything ONCE ONLY. Listen carefully and then answer the questions that follow. Questions 1 to 5 are based on an interview. At the end of the interview you will be given 10 seconds to answer each of the following five questions.
Now listen to the interview.
听力原文：Jassie: Wo! It's very beautiful and I've dreamed of coming here a thousand times. Mr. Bond, it's very kind of you to take us here.
Pauline: Call me Pauline after class, please.
Jassie: OK. Here is the executive mansion of the President of the United States. And from the book, it is on the south side of Pennsylvania Ave. , Washington, D. C. , facing Lafyette Square.
Panline: You've been here for only two weeks. And I think you know a lot about America.
Jassie: I tried to read everything about America when I knew parents would send me here to study. Pauline, would you like to tell me anything else about this building？ Its design is really simple but stately.
Panline: You see. The building is constructed of Virginia freestone. The main entrance, is a portico of high lomic columns reaching from the ground to the roof pediment. The main building is four stories high. The east and west terraces, the executive office, the east wing, and a pent house and a bomb shelter have been added. In the White House, there are four state reception rooms. The East Room is the largest and most formal of them.' Large receptions are usually held in the East Room. The elliptical Blue Room is the scene of many social, diplomatic, and official receptions. The Red Room and the Green Room are used for private and quasi--official gatherings.
Jassie: It was designed by James Hoban, wasn't it？
Pauline:Yes. And George Washington chose the site. It can be said to be the oldest public building in Washing- ton, and its comer stone had been laid in 1792. John Adams was the first President to live here. This buiding was restored after being burned in 1814 by British troops, and the smoke--stained gray stone walls were painted white. Despite popular myth this cognomen was applied to the building some time before it was painted. The name became official when President Theodore Roosevelt had it engraved upon his stationery. Part of the house was rebuilt on a steel--supporting frame. from 1949 to 1952. The grounds cover about 18 acres.
Jassie: With broad lawns, fountains, trees, and gardens, they are more attractive. Eh! Look, Pauline. Nora and Michael are taking photos. Let's go and join them. I figure, this way of teaching is much better than we stay in the classroom reading American Geography.
From the conversation we get the impression that __________.
边界网关协议BGP的报文 (22) 传送。一个外部路由器通过发送 (23) 报文与另一个外部路由器建立邻居关系，如果得到应答，才能周期性地交换路由信息。
（22）
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