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  3. Scientists have established that influenza viruses taken from man can cause the disease in animals. In addition，man can catch th

Scientists have established that influenza viruses taken from man can cause the disease in animals. In addition，man can catch th

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问题     Scientists have established that influenza viruses taken from man can cause the disease in animals. In addition，man can catch the disease from animals. In fact，a great number of wild birds seem to carry the virus without showing any evidence of illness. Some scientists conclude that a large family of influenza viruses may have evolved in the bird kingdom，a group that has been on the earth 100 million years and is able to carry the virus without contracting the disease. These are even convincing evidence to show that virus strains are transmitted from place to place and from continent to continent by migrating birds.  
    It is known that two influenza viruses can recombine when both are present in an animal at the same time. The result of such recombinations is a great variety of strains constraining different H and N spikes. This raises the possibility that a human influenza virus can recombine with an influenza virus form a lower animal to produce an entirely new spike.  
    Research is underway to determine if that is the way that major new strains come into being. Another possibility is that two animal influenza strains may recombine in a pig，for example，to produce a new strain which is transmitted to man.  
What is known about the influenza virus?
选项 A、It was first found in a group of very old birds.
B、All the different strains can be found in wild birds.
C、It existed over 100 million years ago.
D、It can survive in many different places.
答案D
解析 见本文第一段最后一句。有证据显示病菌通过候鸟从一个地方，一个洲传带到另一个地方，另一个洲。由此可以看出病菌可以在不同的地方存活。
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