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  3. The concept of biodiversity encompasses several different levels of biological organization, from the very specific to the most

The concept of biodiversity encompasses several different levels of biological organization, from the very specific to the most

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问题     The concept of biodiversity encompasses several different levels of biological organization, from the very specific to the most general. It has been clear for some time that at all of these levels of organization the rich biodiversity that has always characterized the natural world is today declining. The extinctions or threatened extinctions of many species are but the most visible and well- known manifestation of a deeper and more far-reaching trend.
    Changes in how the land is used are probably the principal contributor to the current decline in biodiversity. The pressures on terrestrial resources and land depend very much on population growth and the demands of early stages of economic development. Moreover, land acquisition, especially. for agriculture and forestry, focuses initially on those areas with the most fertile soils and equable climates, which are often the areas of greatest biological diversity. Deforestation in the humid tropics is probably the best-known current example of rapid land-use change.
    During the decade of the 1970s, vast areas of tropical forest in South America, Africa, and South-east Asia were cleared and converted to agriculture and other uses. In the middle-to-late 1980s, the rates of deforestation in South America slowed dramatically, largely due to economic and tax policy changes in Brazil, but the pace of cutting in Africa and Southeast Asia, though poorly quantified, remains high.
    Globally, the rate of loss of tropical forests for the 1980s has been estimated at about I percent per year, but there is still considerable uncertainty. The rates of extinction of local species that accompany these rapid changes in land cover may soon be far in excess of what is found today, reaching as high as 10, 000 times the natural background rate. Analyses of potential impacts on biodiversity that are based on simple measures of deforested area can provide little more than very general conclusions. Heavy applications of fertilizers and pesticides have the potential of creating additional environmental problems as well as affecting the abundance and viability of the other plants and animals and micro-organisms in the same or adjoining areas.
    In addition, because of the understandable tendency to put the best land into production first, the expansion of agriculture into less fertile areas typically requires heavier applications of chemicals, more extensive site preparation, and other forms of more intensive management. The typical result is increased chemical runoff to the landscape, and with ensuing degradation, additional pressure for expansion, and the like. It is such a cycle that has led to widespread desertification in some parts of the world, primarily through overgrazing that can be compounded by naturally occurring droughts.  
It can be inferred from Paragraph 4 that ______
选项 A、deforestation should usually precede large-scale forestry.
B、the rates of tropical forest loss are established by analyses.
C、fertilizers and pesticides resulted in the extinctions of species.
D、the rates of species extinctions are too complicated to determine.
答案D
解析 题干问：“从第4自然段可以得到的推断是……”。此题可以定位于第4自然段，很明显作者反复说明尽管我们现在有估计，但估计往往是不准确的，从这点推出选项D“物种灭绝的速度往往太过于复杂而不可能确定”为正确选项。而选项A“毁林应该往往在前，之后再大规模的植树”，选项B“热带雨林损失的速度已经得到了科学分析的确认”和选项C“肥料以及杀虫剂往往导致了物种的灭绝”这都不可能从第4自然段的信息得出推导。
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