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Diseases of Agricultural PlantsPlants, like animals, are subject to diseases of various kinds. It has been estimated that some 30,000 different diseases attack our economic plants; forty are known to attack corn, and about as many attack wheat. The results of unchecked plant disease are all too obvious in countries which have marginal food supplies. The problem will soon be more widespread as the population of the world increases at its frightening rate. Even in countries which are now amply fed by their agricultural products there could soon be critical food shortages. It is easy to imagine the consequences of some disastrous attack on one of the major crops; the resulting famines could kill millions of people, and the resulting hardship on other millions could cause political upheavals disastrous to the order of the world.Some plants have relative immunity to a great many diseases, while others have a susceptibility to them. The tolerance of a particular plant changes as the growing conditions change. A blight may be but a local infection easily controlled; on the other hand it can attack particular plants in a whole region or nation. An example is the blight which killed virtually every chestnut tree in North America. Another is the famous potato blight in Ireland in the last century. As a result of that, it was estimated that one million people died of starvation and related ailments.Plant pathologists have made remarkable strides in identifying the pathogens of the various diseases. Bacteria may invade a plant through an infestation of insect parasites carrying the pathogen. A plant can also be inoculated by man. Other diseases might be caused by fungus which attacks the plant in the form of a mold or smut or rust. Frequently such a primary infection will weaken the plant so that a secondary infection may result from its lack of tolerance. The symptoms shown may cause an error in diagnosis, so that treatment may be directed toward bacteria which could be the result of a susceptibility caused by a primary virus infection. According to the passage, some plant diseases can be prevented by ______.
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Smoking Can Increase Depressive Symptoms in TeensWhile some teenagers may puff on cigarettes to "self-medicate" (自我治疗) against the blues (忧郁), scientists at the University of Toronto and the University of Montreal have found that smoking may actually 1 depressive symptoms in some teens."This observational study is one of the few to examine the perceived 2 benefits of smoking among teens," says lead researcher Michael Chariton, a research associate at the Ontario Tobacco Research Unit of the University of Toronto. " 3 cigarettes may appear to have self-medicating effects or to improve mood, in the long 4 we found that teens who started to smoke reported higher depressive symptoms. "As part of the study, some 662 high school teenagers completed up to 20 questionnaires about their use of cigarettes to 5 mood. Secondary schools were selected to provide a mix of French and English participants, urban and rural schools, and schools 6 in high, moderate and low socioeconomic neighborhoods.Participants were divided into three 7 : never smokers; smokers who did not use cigarettes to self-medicate improve mood or physical 8 ; smokers who used cigarettes to self-medicate. Depressive symptoms were measured using a scale that asked how often participants felt too tired to do things; had 9 going to sleep or staying asleep; felt unhappy, sad, or depressed; felt hopeless about the future; felt anxious or tense; and worried too much about things."Smokers who used cigarettes as mood 10 had higher risks of elevated (提升) depressive symptoms 11 teens who had never smoked," says co-researcher Jennifer O"Loughlin, a professor at the University of Montreal Department of Social and Preventive Medicine. "Our study found that teen smokers who reported emotional benefits from smoking are 12 higher risk of depressive symptoms."The 13 between depression and smoking exits 14 among that use cigarettes to feel better. " It"s 15 to emphasize that depressive symptom scores were higher among teenagers who reported emotional benefits from smoking after they began to smoke," says Dr. Chariton.
The Science of Sport1. At the 2004 Olympic Games in Athens, the Chinese athlete Liu Xiang equaled the world record for the 110 meters hurdles (跨栏) when he ran the race in 12.91 seconds. This record time had been set in 1993 by British sprinter (短跑运动员) Colin Jackson and 9 years went by before another athlete was able to run as fast.2. Record-breaking in all track events is slowing down and we appear to be moving much closer to the limits of human performance. Nevertheless, every four years, records which were previously thought to be unbeatable are broken. So what"s behind this, never-ending improvement in performance And how long can we keep breaking records Is there a limit to human performance or will athletes continue to gain seconds3. Most experts agree that it isn"t the athletes" bodies which have changed but the huge advances in sport science which have enabled them to improve their performances. The individual athlete obviously has to have the necessary skill and determination to succeed, but the help of science and technology can be significant. Research has brought a better understanding of the athlete"s body and mind, but the advances in sports equipment technology have also had an important impact on human performance.4. Scientists have shown that an athlete"s body"s needs vary according to the type of sport. This research has helped top sports people to adapt their training program and diet better to their particular needs. Running the marathon and cycling, for example, are endurance (耐力) sports and require a different parathion (硝苯硫磷脂) to that of a 100-meter sprinter. In some sports, changes in techniques have significantly improved performance.5. But in any sport, a player"s success or failure results from a combination of both physical and mental abilities. Most coaches use psychological techniques to help their athletes cope with stress and concentrate on their performance. For example, the English football team listens to music in the changing rooms before a game to help the players to relax and not feel so nervous. Before a difficult match, tennis players are encouraged to use visualization (想像) techniques to build confidence and this is almost as good as practice.6. But as science begins to dominate the sport, are we in danger of losing sight of the heart of the competition, the sporting challenge What"s more, are all these advantages fair Paragragh 3 ______
The Science of Sport1. At the 2004 Olympic Games in Athens, the Chinese athlete Liu Xiang equaled the world record for the 110 meters hurdles (跨栏) when he ran the race in 12.91 seconds. This record time had been set in 1993 by British sprinter (短跑运动员) Colin Jackson and 9 years went by before another athlete was able to run as fast.2. Record-breaking in all track events is slowing down and we appear to be moving much closer to the limits of human performance. Nevertheless, every four years, records which were previously thought to be unbeatable are broken. So what"s behind this, never-ending improvement in performance And how long can we keep breaking records Is there a limit to human performance or will athletes continue to gain seconds3. Most experts agree that it isn"t the athletes" bodies which have changed but the huge advances in sport science which have enabled them to improve their performances. The individual athlete obviously has to have the necessary skill and determination to succeed, but the help of science and technology can be significant. Research has brought a better understanding of the athlete"s body and mind, but the advances in sports equipment technology have also had an important impact on human performance.4. Scientists have shown that an athlete"s body"s needs vary according to the type of sport. This research has helped top sports people to adapt their training program and diet better to their particular needs. Running the marathon and cycling, for example, are endurance (耐力) sports and require a different parathion (硝苯硫磷脂) to that of a 100-meter sprinter. In some sports, changes in techniques have significantly improved performance.5. But in any sport, a player"s success or failure results from a combination of both physical and mental abilities. Most coaches use psychological techniques to help their athletes cope with stress and concentrate on their performance. For example, the English football team listens to music in the changing rooms before a game to help the players to relax and not feel so nervous. Before a difficult match, tennis players are encouraged to use visualization (想像) techniques to build confidence and this is almost as good as practice.6. But as science begins to dominate the sport, are we in danger of losing sight of the heart of the competition, the sporting challenge What"s more, are all these advantages fair Paragragh 4 ______
The Science of Sport1. At the 2004 Olympic Games in Athens, the Chinese athlete Liu Xiang equaled the world record for the 110 meters hurdles (跨栏) when he ran the race in 12.91 seconds. This record time had been set in 1993 by British sprinter (短跑运动员) Colin Jackson and 9 years went by before another athlete was able to run as fast.2. Record-breaking in all track events is slowing down and we appear to be moving much closer to the limits of human performance. Nevertheless, every four years, records which were previously thought to be unbeatable are broken. So what"s behind this, never-ending improvement in performance And how long can we keep breaking records Is there a limit to human performance or will athletes continue to gain seconds3. Most experts agree that it isn"t the athletes" bodies which have changed but the huge advances in sport science which have enabled them to improve their performances. The individual athlete obviously has to have the necessary skill and determination to succeed, but the help of science and technology can be significant. Research has brought a better understanding of the athlete"s body and mind, but the advances in sports equipment technology have also had an important impact on human performance.4. Scientists have shown that an athlete"s body"s needs vary according to the type of sport. This research has helped top sports people to adapt their training program and diet better to their particular needs. Running the marathon and cycling, for example, are endurance (耐力) sports and require a different parathion (硝苯硫磷脂) to that of a 100-meter sprinter. In some sports, changes in techniques have significantly improved performance.5. But in any sport, a player"s success or failure results from a combination of both physical and mental abilities. Most coaches use psychological techniques to help their athletes cope with stress and concentrate on their performance. For example, the English football team listens to music in the changing rooms before a game to help the players to relax and not feel so nervous. Before a difficult match, tennis players are encouraged to use visualization (想像) techniques to build confidence and this is almost as good as practice.6. But as science begins to dominate the sport, are we in danger of losing sight of the heart of the competition, the sporting challenge What"s more, are all these advantages fair Paragragh 2 ______ A. Science may be too important today. B. Sports equipment has been improved a lot. C. Athletes are still breaking records. D. Sport science helps improve athletes" performances. E. Mental training is as important as physical training. F. Different sports require different training programs.
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