题目内容：
共用题干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（测定）the health of the environment by just crawling around and being antsy（坐立不安）.
It has been recognized for decades that ants—which are highly sensitive to ecological change—can provide a near-perfect barometer（气压计）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（构成）so many species.
Where mine sites are being restored,for example,some ant species will recolonize（重新移居到.……）the stripped land more quickly than others.______ (48 ) Australian mining compa- ny 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 Major,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 Major puts it:“That's the great thing about ants.”
Ant surveys are so highly regarded as ecological indicators（指示器）that governments world-wide accept their results when assessing（评估）the environmental impact of mining and tree har- vesting.______(49）.
Why not?Because many companies can't afford the expense or the laboratory time needed to sift（详审）results for a comprehensive survey. The cost stems,also, from the scarcity（缺乏）of ant specialists.______(50)
______(49)
A:This allowed scientists to gauge the pace and progress of the ecological recovery.
B:Yet in other businesses,such as farming 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.
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