The Asian Flu Virus
In 1957, a doctor in Singapore noticed that hospitals were treating an unusual number of influenza-like cases. Influenza is sometimes called "flu" or as "bad cold". He took specimens from the throats of patients in his hospital and was able to find the virus of this influenza.
There are three main types of the influenza virus. The most important of these are types A and B, each of them having several sub-groups. With the instruments at the hospital the doctor recognized that the outbreak was due to 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. 0. published the important news alongside reports of a similar 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 the standard tests. They found that by reproducing itself at a very high speed, the virus had multiplied more than a million times within two days. Continuing their careful tests, the doctors checked the effect of drugs used against all the known sub-groups of type A virus on this virus. None of them gave any protection. This then, was something new: a new influenza virus against which the people of the world had no ready help whatsoever.
Having isolated the virus they were working with, the two doctors now conducted tests on some specially selected animals, which contract influenza in the same way as human beings do. In a short time the usual signs of the disease appeared. These experiments revealed that the new virus spread easily, but that it was not a killer. Scientists, like general public, called it simply "Asian" flu.
The main idea of this passage is that______.
A．a new virus was noticed B．doctors throughout the world treated influenza-like patients C．W. H. 0.paid attention to influenza D．people in Asia were likely to catch influenza