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Malaria is a very serious disease that kills more children under the age of five than any other disease. People get malaria when they are bitten by 1 called mosquitoes. The mosquitoes 2 which enter a person"s blood and cause malaria.
Carter Dibbs is an American doctor who works on the 3 for the United States Agency for International Development. Doctor Dibbs says the parasite that causes malaria is much 4 , such as the virus that causes polio. He says the malaria parasite 5 so that it is more difficult to make a vaccine that is safe and will 6 .
Malaria vaccines are now 7 in Burkina Faso and Mall. Vaccines are being tested on children in Mozambique and Mall. Many organizations are 8 . They include U, S. A. I. D, the American military, American health organizations, 9 .
To make sure that a vaccine will 10 , it must be tested on many people in many different places. Doctor Dibbs says the people who join the vaccine tests are as important to 11 as the scientists.
People are told about the tests during public meetings 12 . Doctor Dibbs says people should 13 that could happen to their bodies if they take the medicine that is being tested. Adults or parents of children must agree to the vaccine test.
Adults receive 14 the vaccine medicine. The children receive either the malaria vaccine or a different medicine that 15 a different disease.
Then health care workers 16 to see if they show any signs of malaria. The results of the tests must be compared to people who have not 17 .
The vaccine is successful if 18 who receive it do not show any signs of malaria for one year.
Then the United States government will be asked to 19 . However, it could still take another five years before 20 to give to all the children in Africa and around the world.

【参考答案】

a licensed vaccine is ready
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drug[解析] 1-20Alcoholism and drug addiction have already reached epidemic proportions in the 21st Century. One of the biggest misconceptions about addiction is that it only affects certain groups within society: poor people from poor neighborhoods and ethnic minorities are more likely to be addicted to alcohol and drugs. The truth is, however, that addiction is blind to race, color and socio economic background. Another fact is that drug and alcohol related crimes are increasing all over the world.There are many reasons why a person might first try drugs. Some of these might include peer pressure from friends, stress and personality characteristics. People take drugs and alcohol because of the elevating or relaxing effects they have on the body otherwise people wouldn t take them in the first place.But as the person develops a habit the chemistry of the brain starts to change and adapt, demanding more and more of the drug as it resists the discomfort of withdrawal. The person becomes an addict and the initial reasons for taking the drug soon pale into insignificance as the need for drugs or alcohol begins to dominate every aspect of the addict s life. Addictions are lifelong illnesses that are very hard to treat. The disturbing fact is that 1 3 of patients who do receive treatment usually relapse within one year.Many scientists believe that addiction is related to our most basic instinct, survival. Since the beginning of time our brain has evolved to ensure the survival of our species. The brain controls behavior by rewarding actions that will ensure survival of the species. For example, the intake of nutrients such as sugars and fats activate taste receptors that in turn activate brain reward mechanisms. The activation of these mechanisms produces certain change in the individual ranging from being in a much better mood to intense pleasure and euphoria. We are far more likely to continue to seek out and eat these nutrients because the brain rewards us for taking the nutrients into the body by releasing chemicals that make us feel good.The problem lies in the fact that these reward systems do not only reward the intake of harmless substances such as sugars and fats. Some chemicals activate brain reward systems directly, bypassing the sensory receptors mediating natural rewards. Caffeine, alcohol and nicotine all activate brain reward mechanisms directly.But other far more harmful drugs such as heroine, crack and cocaine are better at activating brain reward systems, producing a far more powerful effect compared to a feeling of calmness or relaxation after eating a good nutritious meal. The activation is much more intense causing the individual to crave the drug and to focus their activities around taking the drug. The ability of addictive drugs to strongly activate brain reward mechanisms and their ability to chemically alter the normal functioning of these systems can produce an addiction. However, some people become addicted while others do not.Many people drink alcohol or smoke cannabis or even cocaine and other illegal drugs but this does not necessarily make them addicts and not all addicts have the same intensity of addiction.It has been estimated that approximately 10% of any population of any country will tend to have an addictive nature and become addicts of some kind. It is true though that some races, notably Native American Indians and Eskimos, do tend to have higher rates of addiction than others for reasons that are not fully understood. It is also true people who become addicts may be highly intelligent and be extremely motivated but are unable to control their addiction. Addiction is by no means dependent on intelligence. Some of the most skilled and intelligent people might become addicts even though they are fully aware of the detrimental natural of continuing to take drugs or alcohol.The fact is that still we do not know why some people become addicts but others do not, although there are many theories that reason that some people simply have an addictive personality type , being far more susceptible to the reward mechanism that produces addiction while others still believe that it is the addict s lack of will power to refrain from taking drugs or alcohol. The biggest killer though is a person s denial of his or her condition that they believe that they do not have a problem, do not seek help but instead continue the abuse until they have either lost everything or die as the body cannot cope and eventually shuts down.
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Dell says the problem is that it dropped prices too much. But deeper, more threatening forces are also now at play.The first is the resurgence of rivals, which have caught up with Dell s low price model. By driving prices down, Dell has unintentionally cut costs for its rivals too. The supply chain has become as standardized as the components—the money has been wrung out, explains an expert. Dell, by not working through retail outlets, is still more efficient, but the cost benefits that this once brought have been whittled away.The second factor hurting Dell is that growth in the computer business is coming from the consumer market and emerging countries rather than the corporate market, in which Dell sells around 85% of its machines. Increasing sales to consumers is difficult for Dell because individuals tend to want to see and touch computers before buying them. They also like to be able to return the machine easily if it breaks. Dell s tack of retail presence, once ballyhooed as a benefit, has turned into grave disadvantage.A third problem facing Dell is its exclusive use of Intel chips rather than lower-priced ones made by Intel s sworn rivals, AMD. This arrangement lets Dell buy chips inexpensively and benefit from Intel s generous co-marketing programmes. But it has started to harm Dell s sales for higher margin computer servers.
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