题目内容
Passage ThreeQuestions 32 to 35 are based on the passage you have just heard.
查看答案
搜索结果不匹配？点我反馈
更多问题
TEXT B For hundreds of years, farmers have selected and bred plants and animals to favour, or bring out, characteristics they desired.. For example, cows that produced large amounts of milk were selected for breeding, while poor milk producers were not allowed to reproduce. Similarly, horses were bred for speed and strength. Those having these desired characteristics were selected for breeding. Over time, these preferred breeds became more common than earlier, less desired types. This selective breeding is called artificial selection. The theory of evolution by natural selection was put forward in a joint presentation of the views of Charles Darwin and Alfred Russell Wallace before the Linnaean Society of London in 1858. Darwin and Wallace were not the first to suggest that evolution occurred, but their names are linked with the idea of evolution because they proposed the theory of natural selection as the mechanism by Which evolution occurs. We are always more likely to believe in a process when people explain how it happens than if they merely assert that it does. The theory of evolution by means of natural selection is based on three observations. First, as we can see by comparing one cat or human being with another, the members of a species differ from one another; that is, there is variation among individuals of the same species. Second, some of the differences between individuals are inherited. (Other differences are not inherited, but are caused by different environments. For instance, two plants with identical genes may grow to different sizes if one of them is planted in poor soil.) Third, more organisms are born than live to grow up and reproduce: many organisms die as embryos or seeds, as saplings, nestlings, or larvae. The logical conclusion from these three observations is that certain genetic characteristics of an organism will increase its chances of living to grow up and reproduce over the chances of organisms with other characteristics. To take an extreme example, if you have inherited a severe genetic disease of the liver, you have a much lower chance of living to grow up and reproduce than someone born without this disease. Inherited characteristics that improve an organism’s chances of living and reproducing will be more common in the next generation and those that decrease its chances of reproducing will be less common. Various genes or combinations of genes will be naturally selected from one generation to the next (that is, to cause evolution). It is not necessary that all genes affect survival and reproduction; the same result occurs if just some genes make an individual more likely to grow up and reproduce. To summarize: 1. Individuals in a population vary in each generation. 2. Some of these variations are genetic. 3. More individuals are produced than live to grow up and reproduce. 4. Individuals with some genes are more likely to survive and reproduce than those with other genes. Conclusion: From the above four premises it follows that those genetic traits that make their owners more likely to grow up and reproduce will become increasingly common in the population from one generation to the next. The main difference between natural and artificial selection is that human beings______.
Passage TwoQuestions 29 to 31 are based on the passage you have just heard.
Passage ThreeQuestions 32 to 35 are based on the passage you have just heard.
[文档开始] 燥声的危害 燥声是任何一种人都不需要的声音，不论是音乐，还是机器发出来的声音，只要令人生厌，对人们形成干扰，它们就被称为燥声。一般将60分贝作为令人烦恼的音量界限，超过60分贝就会对人体产生种种危害。 强烈的燥声会引起听觉器官的损伤。当你刚从机器轰鸣的厂房出来时，可能会感到耳朵听不清声音了，必须过一会儿才能恢复正常，这便是燥声性耳聋。如果长期在这种环境下工作，会使听力显著下降。 燥声会严重干扰中枢神经正常功能，使人神经衰弱、消化不良，以至恶心、呕吐、头痛，它是现代文明病的一大根源。 燥声还会影响人们的正常工作和生活，使人不易入睡，容易惊醒，产生各种不愉快的感觉，对脑力劳动者和病人的影响就更大了。 [文档结束] 在考生文件夹下，打开文档WDA3_04.DOC，插入文档WTA3_02.DOC，将文档中提供的除标题段文字外的表格数据转换成5行4列的表格，设置列宽为3厘米，行高自动设置，表格中的文字设置为五号，黑体，第一行和第一列的文字居中，其他各单元格中的数字右对齐。存储为文档WDA3_04.DOC。
微信支付 
支付宝支付