In 1957 a doctor in Singapore noticed that hospitals were treating an unusual number of influenzalike cases. Influenza is sometimes called “flu”or a “bad cold”. He took samples from the throats of patients in his hospital and was able to find the virus（病毒）of this influenza. There are three main types of influenza virus. The most important of these are types A and B, each of them having several sub-groups（亚群）. At the hospital the doctor recognized that the outbreak was because of a virus group A, but he did not know the sub-group. He reported the outbreak to the World Health Organization in Geneva. W. H. O. published the important news together with reports of the same kind of outbreak in Hong Kong, where about 15％～20％ of the population had become ill. As soon as the London doctors received the package of throat samples, they began to test them. They found that they could reproduce themselves at a very high speed. Continuing their careful tests, the doctor checked the effect of medicine used against all the known sub-groups of type A virus. On this virus, none of them was of any use. Having separated the virus, the two doctors now made tests on some selected seleceted animals. In a short time the usual signs of the disease appeared. These experiments showed that the new virus spread easily, but that it was not a killer. Scientists, like the general public, called it simply “Asian flu”. 小题1: The Asian flu mentioned in the passage ____. [ ]
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