In Asia, where palm trees are non-native, the trees’ flowers have traditionally been pollinated by hand, which has kept palm fruit productivity unnaturally low. When weevils known to be efficient pollinators of palm flowers were introduced into Asia in 1980, palm fruit productivity increased – by up to fifty percent in some areas – but then decreased sharply in 1984.
Which of the following statements, if true, would best explain the 1984 decrease in productivity?
(A) Prices for palm fruit fell between 1980 and 1984 following the rise in production and a concurrent fall in demand.
(B) Imported trees are often more productive than native trees because the imported ones have left behind their pests and diseases in their native lands.
(C) Rapid increases in productivity tend to deplete trees of nutrients needed for the development of the fruit-producing female flowers.
(D) The weevil population in Asia remained at approximately the same level between 1980 and 1984.
(E) Prior to 1980 another species of insect pollinated the Asian palm trees, but not as efficiently as the species of weevil that was introduced in 1980.
这道题选C 我想问B为何不行？解释说是：B gives no reason for the decrease in productivity of the trees introduced to Asia 我不是很能理解 如果是这样的话C 也没有啊作者: panbangzhu 时间: 2011-11-30 20:13
B Imported trees are often more productive than native trees because the imported ones have left behind their pests and diseases in their native lands
跟楼上说的一样，进口的是虫子而不是树木。所以 imported trees 是无关的
而且问题要解释的是1980年进口虫子之后的一个increase后为什么有一个decrease，B没有解释，或者说按B的说法，因为进口树木把天敌虫子和病害留在了原产地，那么1984年就应该也没有decrease，应该是constant productivity
CRapid increases in productivity tend to deplete trees of nutrients needed for the development of the fruit-producing female flowers说的increase使得耗尽了树木发育雌花的必需的营养（所以会有一个大的decrease），也就解释了1980的increase后为嘛有一个decrease了
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