题目

阅读下列短文，从每题所给的四个选项（A、B、C和D）中，选出最佳选项。     Genetic engineering, in its broadest definition, means to control a species so that a particular trait is increased in the population. A trait is how an organism (有机体) looks or acts or what it does. Having brown eyes is a trait. Flying in circles is a trait. Climbing trees is a trait.     The earliest forms of genetic engineering occurred on farms. People selected seeds from plants that had more fruit production or tastier leaves than other plants of their types. Then they chose to save the seeds from the best of that group to sow the next year. So, year by year, the farmers produced better and better crops. This type of activity probably has been going on since mankind first settled in villages and began making a life for themselves in one location, about 12,000 years ago!     The same sort of thing would have also happened with animals. For example, people chose to eat the animals that didn't have favorable traits and let the animals with the favorable traits reproduce. It was thousands of years before mankind figured out how plants and animals reproduce themselves. With this knowledge, people could pollinate (授粉) plants by hand or keep a pair of animals together in order to deliberately cause an increase in a favorable trait.     It was only in the last 250 years that scientists began figuring out chromosomes (染色体) and genes and the role they play in the way one generation passes its traits on to the next. And it's only been in the last 30 years that scientists have been able to cut out specific genes from one organism and put them in another. It is this 30-year-old technology that is described by the narrow definition of genetic engineering. Mankind has long been able to have a deliberate impact on the world around him. He now possesses the tools to deliberately impact himself. Some people are afraid of what might be done with that power. （1） The text is mainly developed by ________. A . asking questions B . examining differences C . making comparisons D . giving examples （2） Paragraph 2 mainly talks about ________. A . the spread of genetic engineering B . the advantage of genetic engineering C . the original application of genetic engineering D . the popularity of genetic engineering （3） The underlined word "them" in the last paragraph refers to ________. A . specific genes B . special traits C . chromosomes D . scientists （4） What can we learn about genetic engineering from the last paragraph? A . It has a history of 250 years by the narrow definition of genetic engineering. B . Scientists don't know how to make good use of it. C . People have a misunderstanding of it in the past 30 years. D . It is becoming a powerful tool of mankind. 答案： D C A D

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