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练习： 1 .Why are ants compared to ecosystem engineers? A Because they build their own nests. B Because they collect food. C Because their activity affects the environment. D Because they are predators. 2. As predators, ants A prey on small as well as large animals. B collect nutritious food from the soil C collect food as decomposers. D prey on species much higher up the food chain. 3. Dir Sanders study centered on how ants A can manage to thrive in huge numbers. B defend their resources and territory against other predators. C attack those invading animals for survival. D produce such a big impact on the environment. 4. What does paragraph 6 tell us? A Ants bring about a negative influence to an area when their population is small. B Ants bring about a positive influence to an area when their population is small. C Ants predation counteracts the positive influence they may have on an area. D At higher density, ants produce a positive influence on an area. 5. What still remains unclear about ants, according to the last paragraph? | 
