Mental retardation is a condition in which people have lower than normal intelligence and are unable to function at the level expected for their age. People with mental retardation are usually born with it, or it develops early in their life. They may also have some difficulty with dally living skills such as learning to read and write and caring for themselves.
Doctors and other professionals determine that a person has mental retardation based on their intelligence and how well they can do everyday activities. Intelligence is the ability to learn and understand. Levels of intelligence are measured by special tests called intelligence tests. The score a person gets on one of these tests gives a numerical measure of a person's intelligence. This is called an intelligence quotient or IQ.
An average score on an IQ test is about 90 to 110. A person with mental retardation will usually score below 75 on an IQ test.
The IQ test alone does not determine whether someone is mentally retarded. A person must also have trouble with everyday activities such as getting dressed, eating, or washing or learning basic reading, writing, and arithmetic skills.
Mental retardation is not a disease itself. It cannot be cured and it's not contagious. This condition can be caused by several things that injure the brain or don't allow the brain to develop normally. Many times we don't know why a person has mental retardation.
Sometimes it may be caused by genes. Genes are chemical units found in every cell. They carry the instructions telling cells what to do. Sometimes, children receive abnormal genes from their parents.
A defective gene may also develop spontaneously. Neither parent would have passed on the gene, but the gene changes before the baby develops.
Some other problems that can cause mental retardation also happen before a child is born. It is important for the brain to develop properly if a child is to have normal intelligence. "Planning a pregnancy is the most important decision most of us will make in our lifetime. A healthy lifestyle and good medical care should begin before a woman becomes pregnant and continue throughout the pregnancy," says Jodi Rucquoi, a genetic counselor from Connecticut. If a woman abuses alcohol or drugs or doesn't eat well, there is a risk to the developing baby. Also, a premature birth or problems during childbirth can sometimes harm the baby's developing brain. While premature babies are generally fine, there is a greater chance that they may have mental retardation.
In some cases, a young child can develop mental retardation after being sick with a serious infection or other illness, or after suffering a bad head injury.
1. The two major criteria for judging mental retardation are
A. the intelligence quotient and age.
B. the IQ test and mastery of basic reading and writing skills.
C. levels of intelligence and daily living skills.
D. levels of intelligence and arithmetic skills.
2. A person of high intelligence will probably score
A. above 110 on an IQ test.
B. 110 on an IQ test.
C. 90 on an IQ test.
D. below 75 on an IQ test.
3. Which of the following is NOT true of mental retardation?
A. It is not a disease itself.
B. Some of its causes remain unidentified.
C. It is not contagious.
D. It is not incurable.
4. All the following factors may cause mental retardation EXCEPT
A. abnormal genes from parents.
B. a healthy lifestyle before and after a woman' s pregnancy.
C. alcohol or drug abuse by a would-be mother.
D. a premature birth or problems during childbirth.
5. The word “While” in the last sentence of the last but one paragraph can best be replaced by
A Gay Biologist
Molecular biologist Dean Hammer has blue eyes, light brown hair and a good sense of humor. He smokes cigarettes, spends long hours in an old laboratory at the US National Institute of Health, and in his free time climbs up cliffs and points his skis down steep slopes. He also happens to be openly, matter-of-factly gay.
What is it that makes Hammer who he is? What, for that matter, accounts for the talents and traits that make up anyone's personality? Hammer is not content merely to ask such questions; he is trying to answer them as well. A pioneer in the field of molecular psychology, Hammer is exploring the role genes play in governing the very core of our individuality. To a remarkable extent, his work on what might be called the gay, thrill-seeking and quit-smoking genes reflects how own genetic predispositions.
That work, which has appeared mostly in scientific journals, has been gathered into an accessible and quite readable form in Hammer's creative new book, Living with Our Genes. “you have about as much choice in some aspect of your personality.” Hamer and co-author Peter Copeland write in the introductory chapter, “as you do in the shape of your nose or the size of your feet.”
Until recently, research into behavioral genetics was dominated by psychiatrists and psychologists, who based their most compelling conclusions about the importance of genes on studies of identical twins. For example, psychologist Michael Bailey of Northwestern University famously demonstrated that if one identical twin is gay, there is about a 50% likelihood that the other will be too. Seven years ago, Hamer picked up where the twin studies left off, homing in on specific strips of DNA that appear to influence everything from mood to sexual orientation.
Hamer switched to behavioral genetics from basic research, after receiving his doctorate from Harvard, he spent more than a decade studying the biochemistry of a protein that cells use to metabolize heavy metals like copper and zinc. As he was about to turn 40, however, Hamer suddenly realized he had learned as much about the protein as he cared to. “Frankly, I was bored, ”he remembers, “and ready for something new.”
Homosexual behavior, in particular, seemed ripe for exploration because few scientists had dared tackle such an emotionally and politically charged subject. “I'm gay,” Hamer says with a shrug, “but that was not a major motivation. It was more of a question of intellectual curiosity—and the fact that no one else was doing this sort of research”
1. The first paragraph describes Hamer's
A. looks, hobbies and character.
B. viewpoint on homosexuality.
C. unique life-style.
D. scientific research work.
2. Hamer was a
3. What is Hamer doing now?
A. He is exploring the role of genes in deciding one's intelligence.
B. He is exploring the role of genes in deciding one's personality.
C. He is writing a book entitled “Live with Our Genes.”
D. He is trying to answer some questions on a test paper.
4. What happened to Hamer's research interest?
A. He turned to basic research.
B. He sticked to basic research.
C. He turned to behavioral genetics.
D. He sticked to behavioral genetics.
5. According to Hamer, what was one of the main reasons for him to choose homosexual behavior as his research subject?
A. He is a gay and he wants to cure himself.
B. He was curious about it as a scientist.
C. He was curious about it like everyone else.
D. It is a subject that can lead to political success.
The demand for freshwater rises continuously as the world's population grows. From 1940 to 1990, withdrawal of fresh water from rivers, lakes, reservoirs, and other sources has increased fourfold. Of the water consumed each year, 69 percent is used for agriculture, 23 percent for industry, and 8 percent for domestic uses.
Sewage, industrial wastes, and agricultural chemicals such as fertilizers and pesticides are the main causes of water pollution. In 1995, the US Environmental Protection Agency （EPA）. reported that about 37 percent of the country's lakes and estuaries, and 36 percent of its rivers, are too polluted for basic uses such as fishing or swimming, during all or part of the year. In developing nations, over 95 percent of urban sewage is discharged untreated into rivers and bays, creating a major human health hazard.
Water runoff carries fertilizing chemicals such as phosphates and nitrates from agricultural fields and yards into lakes, streams, and rivers. These combine with the phosphates and nitrates from sewage to speed the growth of algae, a type of aquatic plant. The water body may then become choked with decaying algae, which severely depletes the oxygen supply. This process can cause the death of fish and other aquatic life. Runoff also carries toxic pesticides and urban and industrial wastes into lakes and streams.
Erosion, the wearing away of topsoil by wind and rain, also contributes to water pollution. Soil and silt washed from logged hillsides, plowed fields, or construction sites, can clog waterways and kill aquatic vegetation. Even small amounts of silt can eliminate desirable fish species. For example, when logging removes the protective plant cover from hillsides, rain may wash soil and silt into streams, covering the gravel beds that trout or salmon use for spawning.
The marine fisheries supported by ocean ecosystems are an essential source of protein, particularly for people in developing countries; approximately 950 million people worldwide consume fish as their primary source of protein. Yet pollution in coastal bays, estuaries, and wetlands threatens fish stocks already depleted by over fishing. In 1989, 260, 000 barrels of oil was spilled from the oil tanker Exxon Valdez into Alaska's Prince William Sound, a pristine and rich fishing ground. In 1992 there were 8, 790 reported spills in and around U. S. waters, involving 5. 7 million liters （1. 5 million gallons） of oil.
1. According to this passage, which of the following statements is true of yearly water consumption?
A. Most water is used for home cooking.
B. Most water is used for farming.
C. Cities use more water than rural areas.
D. America uses 8 percent of the world water resources.
2. Paragraph 2 suggests all of the following EXCEPT that
A. fish may die because rivers may contain industrial wastes.
B. it may be dangerous to swim in a river because the water may contain pesticides.
C. EPA is responsible for causing serious water pollution in America.
D. water pollution is rather serious in America.
3. Water runoff causes fish to die partly because
A. they are rushed into agricultural fields and yards.
B. they are choked by the water body.
C. the poisonous algae have killed them.
D. the fast-growing algae have used up the oxygen in the water where they live.
4. An important idea of paragraph 4 is that
A. cutting down too many trees may also cause water pollution.
B. erosion is caused by wind and rain alone.
C. there are no longer desirable fish in the world.
D. trout and salmon usually spawn in silt.
5. The main subject of the last paragraph is
A. Fish as a Source of Protein.
B. The Increasing World Oil Production.
C. Oil Spills and Pollution of the Sea.
D. A World-famous Oil Tanker.