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  3. You may not know it, but your body is constantly under attack. The enemies a

You may not know it, but your body is constantly under attack. The enemies a

游客2023-10-15  25
问题     You may not know it, but your body is constantly under attack. The enemies are microscopic invaders called " microbes" or " germs". Microbes, such as bacteria and viruses, are all around you. They live in the air you breathe, on the surface of your skin, and even in the food you eat.
     【B1】______ No. Some germs actually aid certain bodily functions—digestion for one. But some germs can make you very sick. When you get an infection or disease, it is usually because harmful germs have invaded your body and multiplied. They attack and damage your cells.

    Germs spread fast. A single bacterium can multiply into several thousand in just a few hours. If your body had no way of stopping harmful bacteria and other microbes, they would soon overwhelm you. You could not survive for very long. Luckily, your body has defenses against these invaders. Your skin is your first line of defense.
     【B2】______Skin is made of two main layers. They are the inner layer, called the "dermis" , and the outer layer, called the "epidermis". The cells at the surface of the epidermis form a tough, waterproof shield which most germs can not penetrate.
    In addition, organs in the skin help control the number of germs at the surface. The dermis contains thousands of oil glands. The fluid they produce reaches the surface of the skin through pores. Chemicals in the oil help keep germs from multiplying.
     【B3】______Germs can invade through a cut in the skin or through any natural opening of the body. When germs invade, white blood cells arrive to attack them. Two kinds of white blood cells work together to combat disease-causing germs.
    One kind of white blood cell is called the "chemical-warfare" branch of your body’s defenses. These cells produce antibodies chemicals that help combat germs. Antibodies travel through your bloodstream to search out invading germs. They lock onto the germs, giving them a chemical coating that identifies them as harmful.
     【B4】______The antibodies give you "immunity"—the ability to resist infection and disease. Once you have had certain illnesses, such as chicken pox and measles, you probably will never have them again. This is because the white cells will "remember" them and quickly produce antibodies.
     【B5】______A vaccine is a preparation of dead or weakened germs. It does not give you the disease, but it triggers the production of antibodies as if you were actually ill. Vaccines can save your life by helping your body to protect you.
    The other kind of germ-fighting white blood cells are the "foot soldiers" of the body’s defense system. They surround germs and digest them with powerful enzymes. They are able to recognize harmful germs because of the chemical coating the antibodies have given them. The white cells are bigger than most germs. One of them can destroy large numbers of the invaders.
    Some of these white cells die when defending the body. The dead cells, along with body fluids , damaged tissue, and dead germs, form pus. When you see pus around a wound, you know that your white cells have been fighting and dying to protect you.
Questions 61 - 65:
Complete the article with the following sentences. There are two extra sentences that you do not need.
A. How does your skin protect you against germs?
B. Vaccines are dangerous because they give us the diseases.
C. Are all germs harmful?
D. How many different kinds of these cells that fight germs are there?
E. Vaccines can give you immunity against some disease such as smallpox and polio.
F. How do germs get into your body, and what happens when they do?
G. These white cells manufacture a different antibody for each kind of germ. [br] 【B3】
选项
答案 F
解析 本段主要讲述细菌的入侵方式和人体的抵御方法，正是对F项两个问题的回答。因此，本题正确答案为F项。
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