Although we already know a great deal about influenza, and although the World Health Organization is constantly collecting detailed information from its chain of influenza reference laboratories throughout the world, it is extremely difficult for epidemiologists (流行病专家), who study infectious disease, to predict when and where the next flu epidemic will occur, and how severe it will be.
There are three kinds of influenza virus, known as A, B and C. Influenza C virus is relatively stable and causes mild infections that do not spread far through the population. The A and B types are unstable, and are responsible for the epidemics that cause frequent concern. Following any virus attack, the human body builds up antibodies which confer immunity to that strain of virus, but a virus with the capacity to change its character is able to by-pass this protection. Variability is less developed in the influenza B virus, which affects only human beings. An influenza B virus may cause a
A. Man has obtained a great deal of knowledge about influenza
B. The occurrence of influenza is still unpredictable
C. Influenza is being studied extensively and systematically in many countries in the world under the guidance of World Health Organization
D. No reliable treatment of influenza has yet been found.
We have recently heard a great deal about the bad effects of computers on our social and economic institutions. In industry, computers mean automation, and automation means unemployment. The United States, with its extravagant investment in computers, is plagued (使得灾祸，烦恼) by unemployment for unskilled workers. Already computers have begun to displace workers whose tasks are simple. The variety of jobs, formerly done only by humans, that the machine can perform more rapidly, accurately, and economically, increases with each new generation of computers, if we follow this trend, say the pessimists (悲观主义者), we are faced with the prospect of mass unemployment for all but a handful of highly trained, highly intelligent professionals, who will then be more influential and overworked than they are now. Only recently a distinguished English physicist predicted that within twenty years electronic engineers might have to become conscientious objectors in order to prevent these machines from
A. people who refuse to do something for moral reasons
B. objects in the minds of the engineers
C. pessimists who find the whole situation hopeless
D. machines that can prevent computers from ruining us
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