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  3. During the last decade, Val Beasley of the University of Illinois College has led a team wanting to know why the world’s amphibi

During the last decade, Val Beasley of the University of Illinois College has led a team wanting to know why the world’s amphibi

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问题     During the last decade, Val Beasley of the University of Illinois College has led a team wanting to know why the world’s amphibian(两栖动物) populations have been decreasing or riddled with deformed limbs.
    Evidence from his and other teams points to increasing numbers of common parasites as an important cause. However, the problems facing amphibian habitats really pose a distressing example of ecosystems out of balance because of human activity, according to Beasley, a professor of biosciences and executive director of Wildlife and Ecosystem Health. Beasley’s main collaborators, postdoctoral researcher Anna M. Schotthoefer and Rebecca A. Cole, a scientist with the National Wildlife Health Center in Madison, Wis. , say they agree.
    A series of their research projects -— two published in 2003 and another that will appear as a book chapter this year — dramatically refine the data on parasitic activity and argue that physically and chemically induced changes of aquatic habitats are taking a toll.
    "We have to be asking what human activities are contributing to imbalances in these ecosystems to set the stage for more severe infections, " Beasley said. "It’s becoming a serious question of how we can better manage landscapes, streams, wetlands, ponds and lakes. Frogs are among the first animals that young children see in a healthy wild place, but they are not finding them in the same numbers as in past years. "
    Tadpoles (蝌蚪) of many species feed on algae converting the material into the protein, fat and other nutrients that are needed by other creatures higher in the food chain, Beasley said. Amphibians are clearly important players in ecosystem functioning, he added. "The frogs that develop from tadpoles subsequently eat up thousands of insects," he said, "The frogs themselves are also important prey for reptiles, birds and mammals."
    In the study funded by Chicago Zoological Society, Beasley’s team noted that Midwest landowners hollow out their ponds so that deep water prevents the establishment of aquatic plants.
Such a practice allows for easier boating, swimming and fishing, but by eliminating aquatic plants, the habitat becomes structurally barren. Herbicide use also aggravates the problem and produces chemical changes. Plant-derived oxygen is reduced, and herbicides also may have direct toxic effects on tadpoles and other animals, Beasley said. The lack of vegetation may expose tadpoles to more parasites coming from the infected snails, because the tadpoles can’t hide or use the vegetation to brush off the parasites, Schotthoefer said.
    So while the parasites seem to contribute to declines and deformation in frog populations,the challenge is to find management approaches that put balance back into amphibian ecosystems, Beasley said.
We can conclude from the text that
选项 A、the government is seeking a solution to the problems of amphibian habitats.
B、tadpoles can make use of aquatic plants to get rid of parasites.
C、parasites can cause great damage to frogs’ nerve center.
D、tadpoles are infected after they eat infected snails.
答案B
解析 倒数第二段指出：水生植被的缺少还可能使蝌蚪接触到更多来自染病蜗牛的寄生虫，因为蝌蚪不能躲藏或利用植被拂去这些寄生虫。由此可推知水生植物的一个用处是帮助蝌蚪除掉寄生虫，故[B]为答案。根据末段排除[A]项。[C]项和[D]项属于过度推断。
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