UNIT 1There are two factors which determine an individual's intelligence. The first is the sort of brain he is born with. Human brains differ considerably, some being more capable than others. But no matter how good a brain he has to begin with, an individual will have a low order of intelligence unless he has opportunities to learn. So the second factor is what happens to the individual—the sort of environment in which he is brought up. If an individual is handicapped environmentally, it is likely that his brain will fail to develop and he will never attain the level of intelligence of which he is capable. The importance of environment in determining an individual's intelligence can be demonstrated by the case history of the identical twins, Peter and John. When the twins were three months old, their parents died, and they were placed in separate foster homes. Peter was reared by parents of low intelligence in an isolated community with poor educational opportunities. John, however, was educated in the home of well-to-do parents who had been to college. This environmental difference continued until the twins were in their late teens, when they were given tests to measure their intelligence. John's I.Q. was 125, twenty-five points higher than the average and fully forty points higher than his identical brother.有两个因素决定一个人的智力。
首先是他出生时带的大脑排序。
人类的大脑彼此之间有很大不同，有的有比别人多的能力。
但不管他出生时有多好的大脑，个人将有低下的智力，除非他有学习的机会。
因此第二个因素是在他长大的环境中发生了什么。
如果一个人在环境方面有障碍，很可能他的大脑将无法发展，他将永远不会他能够达到的智力水平。
同卵双胞胎彼得和约翰的经历可以说明环境对于一个人智力发展的重要性。
当这对双胞胎三个月大，他们的父母去世了，他们分别被安置在不同的寄养家庭。
彼得被寄养在一个孤立的社区并且教育机会少，低智商的父母家中。
然而约翰，在生活富裕、上过大学的父母家中接受教育。
这种环境差异继续到这对双胞胎十几岁时，当测试他们的智力时。
约翰的I.Q.是125，高于普通人二十五点，比他的兄弟高出整整四十分。
UNIT 2Recent studies of the human brain have resulted in some interesting discoveries. Scientists believe that a way to improve the power of the brain may soon be possible.Scientists have discovered that the brain can make its own drugs. The brain contains a protein substance which can act directly on the brain to change aspects of mental activity. Some may change or improve, for example, creativity,intelligence, imagination, and good memory.Chemicals found in the brain carry messages. In recent years scientists have found chemicals that affect mood, memory and other happenings of the mind. About 25 have been found so far.Today the role of chemicals and protein substance in human behaviour is creating much interest. Research seems to show that they may help control insomnia, pain, and mental illness. They have a great capacity to stimulate the brain to conquer deficiencies. They also improve the qualities of memory and learning already in the brain. They hold the secret to mood and emotion. Some day there may be a chemical way to create a better and more efficient brain.最近对人类大脑的研究报告中有一些有趣的发现：科学家认为一种改善大脑功能的方法可能很快成为可能。
科学家们发现大脑可以产生自己的药物。
大脑中含有一种蛋白物质，它可以直接作用于大脑以改变心理活动的各个方面。
有些可能会改变或改善，例如，创造力，智力，想象力和良好的记忆力。
在大脑中发现的化学物质携带着消息。
近年来科学家们已发现影响情绪，记忆和大脑活动的其它化学物质。
目前约25种已被发现。
今天，化学物质和蛋白质物质在人类行为的作用引起了人们很大的兴趣。
研究似乎表明，它们可能有助于控制失眠，疼痛，和精神病。
它们有一个巨大的能力来刺激大脑克服不足。
它们还提高记忆和大脑中应经存在的学习质量。
他们保持情绪和情感的秘密。
将来有一天，有可能会有一种化学方法来创造一个更好、更有效率的大脑。
Unit 3By measuring the amount of HIV’s genetic material i n various representative tissue samples from infected peop le, and extrapolating form these samples to the entire bod y, Haase estimates that at most 1 in 2,500 cells, maybe fe wer, isinfected with HIV. This is nowhere near enough for direct cell killing to account for the depletion in their numbers th at leads to AIDS.通过测试被感染者具有代表性的组织样本中HIV 的遗传材料，从这些样本推算整个身体，哈泽估计，最多1 ／2500，或许更少，感染了HIV。
这对于直接杀死细胞引起细胞大量消亡而导致艾滋病是远远不够的。
Haase says that his own work now shows that large n umbers of CD4 cell are becoming trapped in lymph tissue , and he believes that HIV also disrupts the production of new cells. In common with a number of other researchers, he alsobelieves that HIV may cause the loss of uninfected CD4 c ells by triggering abnormally high levels of cell suicide,or apoptosis-a separate process that has been a subject of res earch throughout the 1990s .哈泽说自己现在的工作表明，大量的CD4细胞被困在淋巴组织，而且他认为，艾滋病病毒会破坏新细胞的产生。
研究人员普遍认为，艾滋病毒可以通过触发细胞自毁或消亡，导致未受感染的CD4细胞减少。
在20世纪90年代这一过程曾是一个研究课题。
Taken together, these findings clearly suggest that H IV keeps the immune system in a state of constant activati on,and unbalances it in four ways :by trapping mature cells ,by stopping the production of new cells, by triggering abnormally high rates of apoptosis and by killing a small but significant number of cells directly. Their combined i mpact leaves the immune system depleted and unable to c ope with opportunistic infections.总之，这些研究结果清楚地表明，艾滋病病毒使免疫系统处于激活状态，不平衡的方式有四种：通过捕获成熟细胞，停止生产新的细胞，通过触发异常的高细胞凋亡率，直接杀死小但是数量大的细胞。