题目内容：
第50题_________
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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答案解析：