工程硕士英语unit9完型答案及翻译.doc

Unit 9 Exercises III Cloze Test B Worldwide, almost 99% of the human food supply is plant species and 8 livestock species, small numbers when _ compared with ___ the estimated 10-30 million species _ inhabiting _ our biosphere. Introducing genes from various organisms into crops and livestock has long been regarded as a promising way to _ ensure _ the continued productivity of agriculture and forestry. Then, too, the substitution or addition of diverse genes into agricultural and forestry species may, as Raven has suggested, be a _ way _ to use the undiscovered resources of biodiversity in the _ service __ of social and economic development. Genetic engineering technology has dramatically reduced the time _requested_ for the development of new commercial varieties of crops. Some investigators have suggested that the use of genetic markers could reduce __ the usual 10-15-year breeding _ cycles __ to only 2-3 years. Genetic engineering is rapidly _ replacing __ traditional plant breeding programs and has become the mainstay of agricultural crop improvement. __ Since __ 1986, 2053 field trials have led to the release of transgenic plants into natural ecosystems around the world. Recent advances in the genetic engineering of plants, animals, and microorganism, _ including viruses, are encouraging and show _ promise _ for further development. _ Meanwhile _, research efforts are increasing at university industry, and government laboratories. In addition to the _ perceived _ benefits of genetic engineering for the industrialized nations, proponents __ advocate _ the use of genetic engineering to improve agriculture in developing countries. This _ strategy _ might help these countries bypass expensive, high-input crop production and move their traditional agriculture toward low-input sustainable _ practice __. Many scientists, however, have expressed __ concern _ regarding the possible environmental risks. Many have asserted that the release of genetically engineered org