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  3. Why is the close planting of trees of the same species avoided in modern orchards and forests? The relative stability of the hu

Why is the close planting of trees of the same species avoided in modern orchards and forests? The relative stability of the hu

admin2009-04-23  86
问题 Why is the close planting of trees of the same species avoided in modern orchards and forests?
The relative stability of the human population has been upset by ______.
选项 A、the proportion of the reproductive age group
B、the influenza epidemic
C、advances in medical science
D、the Black Death in Europe
答案C
解析 细节题。见文章第二段第三句The relative stability of the human population has been upset by advances in medical science，所以答案为C。
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