练习：
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.
答案与题解：
1.F “空1”前面的句子有certain species，后面的句子有still others，这一定是英语中的“some/ certain一others一still others”的固定结构。仅从这一点判断，F是答案。
2.D 决定哪个句子填入“空2"的一个方法是排除法。选项A、B,C,F(F已选为“空1”的答案)的内容与“空2”前后的句子意思上都不连贯。选项E有些突如其来。只有选项D符合上下文的意思。this：指前面句子中的can determine how "stressed" the land is。
3.A 选项A中的ecological recovery与前面一句中的recolonize相呼应，提示选项A的句子是前面句子的后续句。
4.B 选项B中的关键词。ther businesses,farming,property提示，选项B的句子是前面句子的后续句，因为前面句子有mining ,tree harvesting，也是businesses。蚂蚁分析法已被mining和tree harvesting等行业广泛接受，但在farming和property行业中的应用还不普遍。
5.C 本题的答案很自然会选C，因为scarcity，当然就贵了。此外，those指的是前一句的specialists，进一步证明选项C是正确的。