2009年12月大学英语四级预测试卷(江涛)

　　Part Ⅰ Writing (30 minutes)
　　Directions: For this part, you are allowed 30 minutes to write a composition on the topic College Graduates Work as Village Officials. You should write at least 150 words according to the outline given below in Chinese:
　　1. 你是否认为大学生当村官是个好主意
　　2. 大学生能给乡村提供些什么来源：和谐英语学习网
　　3. 大学生能从村官职位中获得什么
　　注意：此部分试题在答题卡1上。
　　Part Ⅱ Reading Comprehension (Skimming and Scanning) (15 minutes)
　　Directions: In this part, you will have 15 minutes to go over the passage quickly and answer the questions on Answer Sheet 1. For questions 1-7, choose the best answer from the four choices marked A), B), C) and D). For questions 8-10, complete the sentences with the information given in the passage.
　　How Infectious Diseases Work
　　The human body is both surrounded and inhabited by billions of microorganisms. Most microorganisms are harmless or even beneficial; for example, bacteria that normally live in the digestive system help digest food. Occasionally, however, a microorganism capable of causing a disease invades the body. Diseases caused by such microorganisms are called infectious diseases.
　　Infectious diseases are contagious; that is, they can be passed from one person to another. They can be transmitted by skin contact, through body fluids, in contaminated food or drink, or via airborne particles containing the microorganisms, although the pathways and ease of transmission vary by disease.
　　Animal or insect bites are another means of transmission. The two most common types of infectious diseases are bacterial infections and viral infections.
　　Disease-causing, or pathogenic, bacteria either attack the body’s tissues directly or cause damage by secreting poisonous substances called toxins. Fortunately, bacterial infections are often curable. Certain bacteria can be killed by drugs; other bacterial diseases can be prevented by vaccination.
　　Viruses are the smallest known microorganisms. They are responsible for diseases as relatively harmless as the common cold and as serious as meningitis. Viruses live and reproduce only within living cells, and only certain cells are susceptible to a specific virus. You can be host to many viruses without suffering any adverse effects, but if enough cells are attacked, you will become sick.
　　There is no effective medical treatment for most viral infections. Because a virus lives inside a cell, any treatment designed to kill the virus is also likely to harm the cell. In addition, there are thousands of different viruses—each one with different properties—and an agent effective against one virus probably will not affect the others. Although there are vaccinations to protect against some viral diseases, therapy for most viral diseases is limited to treating the symptoms.
　　In this article, we’ll focus on the many facets of infectious diseases, starting with how the body defends against them.
　　The Body’s Defenses
　　Despite the prevalence of disease-causing microorganisms, the body is not defenseless against these invaders. The body fights infections in three ways: by preventing the organisms from entering the body, by attacking those that do manage to enter, and by inactivating those organisms it cannot kill.
　　Sometimes, too, the body fights disease by developing defensive symptoms. Fever is an example. During an illness, the body’s temperature regulator may respond to the illness by raising the body’s temperature. Some researchers believe that this is an effective response because the microorganisms causing the disease may not be able to survive the higher body temperature.
　　The skin is the first barrier that guards the underlying tissues of the body. Where there are natural openings in the skin, there are also defenses. For example, tear glands in the eyes secrete and bathe the eyes with fluid that contains bacteria-fighting components. The salivary glands in the mouth and the tonsils in the throat help prevent microorganisms from attacking the mouth and throat.
　　Many openings, as well as internal passages, in the body are lined with mucous membranes. These delicate layers produce mucus, a slippery secretion that moistens and protects by repelling or trapping microorganisms.
　　Internally, certain body organs fight infection. For instance, the liver and the spleen (a large glandlike organ located in the abdomen) filter out harmful substances from the blood flowing through them. The lining of the stomach produces acids that attack germs in food that has been eaten. The body’s lymph system manufactures white blood cells, which attack and kill invading organisms.
　　Now let’s get even more specific in our look at the body’s defenses. We’ll start by describing the lymph system.
　　The Lymph System
　　The lymph system is a network of vessels that carry lymph, a watery fluid containing white blood cells, throughout the body. Lymph drains from the blood vessels and body tissues, carrying away waste products. The waste products are filtered out of the lymph by small structures called lymph nodes. Within the lymph nodes, harmful microorganisms are trapped, attacked, and destroyed by white blood cells. This is one of the body’s primary and most efficient lines of defense.
　　Antibodies are manufactured in the lymph system. Antibodies are protective substances that the body produces in response to invasion by a hostile organism or the presence of a foreign substance. Antibodies counteract some invading bacteria and viruses by inactivating them so that they are powerless. Antibodies that neutralize toxins (poisons) produced by bacteria are called antitoxins.
　　The body’s production of white blood cells and antibodies in response to an invading organism is called the immune reaction. Immunity is the body’s ability to resist an invasion of disease-causing bacteria and viruses. Once antibodies have been made to fight a certain type of microorganism, that microorganism usually no longer poses a threat to the body. That is why one attack of a disease often prevents its recurrence down the road. The first attack causes antibodies to be produced, and these antibodies protect the system against future attacks.
　　There are ways to help the body’s own defenses work. One is immunization, something all of us have experience with.
　　Immunization
　　Immunity can be provided artificially by vaccination and other forms of immunization. A vaccine is a preparation containing the offending organism—usually in a weakened form that will not cause the actual disease. When introduced into the body, the vaccine stimulates the body to produce antibodies against the disease. These antibodies often remain in the system for life, and the body is thus prepared to resist the actual disease.
　　A number of viral diseases can be prevented by immunization. There are vaccines for polio, measles, rubella (German measles), mumps, some strains of influenza, and chicken pox. A vaccine against the organism Hemophilus influenzae also is available. This vaccine prevents the most common cause of bacterial meningitis in children.
　　注意：此部分试题请在答题卡1上作答。
　　1. According to the passage, most microorganisms in human body are ________.
　　A) beneficial
　　B) harmless or even beneficial
　　C) harmless
　　D) harmful
　　2. Infectious diseases cannot be transmitted ________.
　　A) by skin contact
　　B) in contaminated food
　　C) by insect bites
　　D) through common fluid
　　3. Some bacterial diseases can be cured by ________.
　　A) drugs
　　B) vaccination
　　C) toxins
　　D) viruses
　　4. Viruses live and reproduce ________.
　　A) in microorganisms
　　B) only within living cells
　　C) only in living microorganisms
　　D) in cells
　　5. For most ________, there is no effective medical treatment.
　　A) infections
　　B) bacterial infections
　　C) viral infections
　　D) infectious diseases
　　6. How many ways are mentioned in the passage as to how the body fights infections?
　　A) 2
　　B) 3
　　C) 4
　　D) 5
　　7. The ________ is the first barrier of the body’s defenses.
　　A) salivary gland
　　B) tear gland
　　C) liver
　　D) skin
　　8. The lymph system is ________ that carry lymph, a watery fluid containing white blood cells, throughout the body.
　　9. The immune reaction means the body’s production of white blood cells and antibodies in response to ________.
　　10. If antibodies have been made to fight a certain type of microorganism, they can protect the system_________.