求助OG12-18

木寻云

In Asia, where palm trees are nonnative, 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 50 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.







正确答案：C 因为营养被吸干了，所以productivity下降了；


我想问：D 为什么不可以？


我当时排除C 是觉得上文没有提到nutrients，所以无关；
我之所以选D 是觉得文中说weevils的引进 导致了 手工授粉变昆虫授粉 所以 productivity上升了；


那么后来下降了，我认为根据文本，weevils导致productivity上升，那么productivity的下降也与weevils有关。
所以选了D，
由于productivity上升，而之后weevils数量跟不上，导致后来又decrease了。


大家帮我解释一下吧>____<万分感激呐！