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  3. An epidemic of swine flu (猪流感) has recently developed in Mexico and the United States, says the CDC. Swine flu has killed many p

An epidemic of swine flu (猪流感) has recently developed in Mexico and the United States, says the CDC. Swine flu has killed many p

admin2012-02-02  66
问题     An epidemic of swine flu (猪流感) has recently developed in Mexico and the United States, says the CDC. Swine flu has killed many people, and the outbreak has features that suggest it could become a global pandemic (瘟疫). A pandemic is an epidemic that spreads around the whole world. Pandemics also often cause more severe disease than epidemics.
    Flu is a disease caused by the influenza virus. Humans, pigs, birds and other animals all can be infected by influenza viruses. Typically, influenza viruses can infect only one species, so the influenza viruses of humans are different from those of pigs and birds. However, sometimes a virus can infect more than one species. For examples, pigs sometimes can be infected not only with pig influenza viruses, but also with human and bird influenza viruses. Then these viruses can come up to one another secretly and swap (交换) genes, creating new viruses that have a mix of genes — from human, pig, and bird viruses. That is what has happened with this new swine flu virus.
    Sometimes this swapping of genes allows a virus that was originally able to infect only pigs or only birds to also infect humans. When that happens, we refer to the illness as "swine flu" or "bird flu". This current virus could actually be called "swine/bird flu", since it has some genes from pig flu viruses and other genes from bird flu viruses.
    Most viruses that cause swine flu or bird flu are very hard to pass from one human to another: they don’t cause epidemics. Sometimes, however, further changes in genes create a virus that can spread rapidly among humans, and can produce a more severe illness. One reason this illness is more severe is that the virus is so new. The regular flu that comes each year is caused by a regular human influenza virus that often has similarities to the viruses that have caused the flu in years past, so people have some degree of immunity to the latest virus. The unusual swine flu or bird flu viruses that develop the ability for person-to-person spread are so different that people have little or no immunity to them.
    The worst global pandemic in modern times was the influenza pandemic of 1918 to 1919. It affected about a third of the human race, and killed at least 40 million people in less than a year — more than those who have been killed by AIDS in three decades. The world economy went into a deep recession. The average length of life dropped for 10 years.
    Unfortunately, the new swine flu virus can be transmitted between humans. It is not clear yet how easily it is transmitted, nor how it is transmitted. Almost surely it is transmitted by sneezing and coughing, and by skin-to-skin contact with an infected person.
Which of the following is true about the present swine flu viruses?
选项 A、The viruses can infect different species.
B、The genes of the viruses come from pigs.
C、The viruses mix genes from different species.
D、The genes of the viruses were made artificially.
答案A
解析 题干问的是目前的猪流感病毒的情况。原文从第二段开始对这种新流感病毒分析描述。第三句说，通常情况下，流感病毒只感染一个物种。第四句说，有时一种病毒却可能感染多个物种。然后举例，最后一句说这次的新型猪流感病毒就属于这种情况。由后文也可知道，这种新型猪流感病毒能感染人、猪和鸟类。所以[A]项正确。第二段倒数第二句中说，本次猪流感病毒的基因混合了猪、人和鸟类身上的三种流感病毒的基因，所以排除[B]。它的基因不是混合了多个物种的基因，而是混合了这些物种身上的不同病毒的基因，排除[C]。原文中没有提及这种病毒是否是人工制造的，排除[D]。
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