| Scientists have learned a great deal about the kinds of food people need. They say that there are several kinds of food that people should eat every day. What are these classes of food They are 1) green vegetables of all kinds, such as string beans, peas, lettuces, and cabbages; 2) fruit, such as apples, peaches and bananas; 3) other vegetables, examples of these are beets, onions, carrots, tomatoes and so on; 4) meat of all kinds, fish and eggs; 5) milk and food made from milk, such as butter, cheese and ice-cream; 6) bread or cereal. Rice is also in this class of food. People in different countries and different areas of the world eat different kinds of things. Scientists say that none of these differences are really important. It doesn’t matter whether food is eaten raw or cooked, canned, or frozen. It doesn’t matter if a person eats dinner at four o’clock in the afternoon or at eleven o’clock at night. The important thing, they say, is that every day a person should eat something from each of these kinds of food. There are two problems, then, in feeding the ever-increasing number of people on earth. The first is to find some ways to feed the world population sd that no one is hungry. The second is to make sure that people everywhere have the right kinds of food to make them grow to be strong and healthy. |
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.
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