Grassland songbirds often nest in the same grassland-wetland complexes as waterfowl, particularly in a certain part of those complexes, namely, upland habitats surrounding wetlands. Although some wildlife management procedures directed at waterfowl, such as habitat enhancement or restoration, may also benefit songbirds , the impact of others, especially the control of waterfowl predators, remains difficult to predict. For example, most predators of waterfowl nests prey opportunistically on songbird nests, and removing these predators could directly increase songbird nesting success. Alternatively, small mammals such as mice and ground squirrels are important in the diet of many waterfowl-nest predators and can themselves be important predators of songbird nets. Thus. Removing waterfowl-nest predators could affect songbird nesting success through subsequent increases in small-mammal populations.
In 1995 and 1996, researchers trapped and removed certain waterfowlnest predators. primary raccoons and striped skunks, then observed subsequent survival rates for songbird nests. Surprisingly. They observed no significant effect on songbird nesting success. This may be due to several factors. Neither raccoons nor striped skunks consume ground squirrels, which are important predators of songbird nests. Thus, their removal may not have led to significant increases in populations of smaller predators. Additionally, both raccoons and striped skunks prefer wetlands and spend little time in upland habitats; removing these species may not have increased the nesting success of songbirds in the uplands enough to allow detection.
The primary purpose of the passage is to

*内容概述:
文章开头说女性的草根运动时期和他们对新文明意识的看法的核心来自于美国在大推进时期的社会改革。接着进一步解释在这一时期中产白人女性改革者取得的成就。接下来笔锋一转,在童工问 题上不同阶级女性看法不同。改革者认为必须剔除,但工人阶级则认为童工法会让家庭里干活的人变少,生活难以为继。最后是作者的评价,承认改革者要求不适用童工是正确的,但他们没有考 虑到工人阶级的家庭经济状况
*文章类型:人文历史
*文章套路:对比解释说明
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*题目类型:主旨题
*选项分析:主旨题去看全文内容概述。本文的目的就是文章的结尾处说的中产阶级改革者没能够理解公认阶级的经济状况。因此正确答案是D

