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  3. Ants as a Barometer of Ecological Change At picnics, ants are pests. But they have their uses. In industries such as mining, far

Ants as a Barometer of Ecological Change At picnics, ants are pests. But they have their uses. In industries such as mining, far

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问题 Ants as a Barometer of Ecological Change
At picnics, ants are pests. But they have their uses. In industries such as mining, farming and forestry, they can help gauge the health of the environment by just crawling around and being antsy.
It has been recognized for decades that ants--which are highly sensitive to ecological change--can provide a near-perfect barometer of the state of an ecosystem. Only certain species, for instance, will continue to thrive at a forest site that has been cleared of trees.
(46)And still others will move in and take up residence.
By looking at which species populate a deforested area, scientists can determine how "stressed" the land is.(47)Ants are used simply because they are so common and comprise so many species.
Where mine sites are being restored, for example, some ant species will recolonize the stripped land more quickly than others.(48)Australian mining company Capricorn Coal Management has been successfully using ant surveys for years to determine the rate of recovery of land that it is replanting near its German Creek mine in Queensland,
Ant surveys also have been used with mine-site recovery projects in Africa and Brazil, where warm climates encourage dense and diverse ant populations. "We found it worked extremely well there," says Jonathan Majer, a professor of environmental biology. Yet the surveys are perfectly suited to climates throughout Asia, he says, because ants are so common throughout the region. As Majer puts it: "That’s the great thing about ants."
Ant surveys are so highly-regarded as ecological indicators that governments worldwide accept their results when assessing the environmental impact of mining and tree harvesting.
(49)
Why not? Because many companies can’t afford the expense or the laboratory time needed to sift results for a comprehensive survey. The cost stems, also, from the scarcity of ant specialists.
(50)

A  This allowed scientists to gauge the pace and progress of the ecological recovery.
B  Yet in other businesses, such as fanning and property development, ant surveys aren’t used widely.
C  Employing those people are expensive.
D  They do this by sorting the ants, counting their numbers and comparing the results with those of earlier surveys.
E  The evolution of ant species may have a strong impact on our ecosystem.
F  Others will die out for lack of food.
选项
答案C
解析 本题的答案很自然会选C，因为scarcity,当然就贵了。此外，thos指的是前一句的specialists，进一步证明选项C是正确的。
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