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  3. Recently, researchers investigated the foraging profiles of bird species in two separate eucalyptus forests in Australia: Dryand

Recently, researchers investigated the foraging profiles of bird species in two separate eucalyptus forests in Australia: Dryand

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问题     Recently, researchers investigated the foraging profiles of bird species in two separate eucalyptus forests in Australia: Dryandra in Western Australia and the Southern Tablelands, roughly 3000 km west in New South Wales. Despite their geographical separation, there is a broad overlap in species between the two locations. However, at Dryandra, a much larger proportion of species (61 percent) than at the Southern Tablelands (34 percent) are ground foragers.
    The high proportion of ground foragers in Dryandra might be explained by the openness of habitats there, that is, the absence of dense ground vegetation, and the lack of a continuous shrub layer. Ground foraging appears to be facilitated by an open habitat with area of bare ground. However, the researchers found that the Tablelands were also open with sparse to dense litter layers, abundant in woody debris, and had discontinuous or absent ground and shrub layers. Thus, differences in habitat structures between these areas and Dryandra cannot entirely explain the greater abundance of ground foragers in Dryandra.
    The researchers offered several hypotheses to explain the difference. First, there may be important differences in habitat structure that are not revealed by casual observation. For example, differences in tree heights and canopy complexity may contribute to differences in species richness and foraging behavior among bark- and foliage-foraging birds. Second, despite structural similarities, it is possible that there are differences between habitats in the abundance or availability of litter and ground-dwelling prey. Such differences, if they exist, may indicate fundamental differences between eucalypt ecosystems in how and where energy and nutrients are cycled, as well as in overall productivity. Finally, the differences in foraging profiles between Dryandra and Tablelands may be the result of historical changes in bird species as a consequence of changed grazing and fire regimens, the impact of introduced predators, such as foxes and feral cats, and logging following European settlement. The greatest impact of these processes is on ground-foraging and ground-nesting birds. Dryandra has not been free of these changes, but the impact may have been less or more recent with the result that Dryandra may retain a more natural or complete bird diversity relative to the Tablelands.
Which of the following best describes the organization of the second paragraph?
选项 A、A thesis is proposed and supporting examples are provided.
B、A thesis is presented, considered, and then rejected.
C、Opposing views are described and the evidence on which they are based is evaluated.
D、An argument is described, rejected, and then an alternative is presented.
E、A hypothesis is presented, weighed, qualified, and then reaffirmed.
答案B
解析 第二段属于驳论文的结构。第一句给出观点，认为是德兰德拉林地的地面开阔导致地面觅食者更多。第二句给出理由，将地面的开阔和觅食者建立联系。第三四句However取反，反驳之前的观点。整段只在反驳，而没有提出新观点，因此选项B正确。
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