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  3. Why is the close planting of trees of the same species avoided in modern orchards and forests? Attempts to introduce myxomatosi

Why is the close planting of trees of the same species avoided in modern orchards and forests? Attempts to introduce myxomatosi

admin2009-04-23  46
问题 Why is the close planting of trees of the same species avoided in modern orchards and forests?
Attempts to introduce myxomatosis into New Zealand to control rabbit population have failed, mainly because ______.
选项 A、increasing resistance to the disease is becoming apparent
B、there are no species of insects transmitting the disease in this country
C、flea and mosquito without the disease are absent in this country
D、the myxomatosis virus has been introduced into Australia
答案B
解析 因果关系题。见文章第三段最后一句Attempts to introduce myxomatosis into New Zealand as a means of rabbit population control have failed，mainly because the species of flea and mosquito which transmit the disease are absent in this country，没有传染的媒介，所以答案为B。
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