题目详情:

[单项选择]亚洲并非棕榈树的原产地，在这儿传统上用手工为棕榈树传递花粉，这种办法使棕榈果实产量非常低。当1980年将作为棕榈花的有效授粉者而被熟知的象鼻虫引进亚洲后，棕榈的产量上升——在某些地区上升了50%，但在1984年急剧下降。
以下哪一项如果是正确的，将对1984．年产量的下降提出最好的解释( )
A. 随着产量的上升同时需求下降，1980～1984年之间，棕榈果实的价格持续下跌
B. 进口树经常比本地树树产量更大，因为进口树将它们的害虫与疾病留在它们本国的土地上
C. 产量的迅速提高耗尽了培育果实的雌花生长需要的营养物质
D. 在1980～1984．年之间，亚洲象鼻虫的数量保持在相同的水平上

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[单选题]When George Osbome,Chancellor of the Exchequer,is spotted outside Westminster,he is very often making an appearance on a building site,wearing a fluorescent safety jacket.It was no surprise to hear him claim once again,in his budget speech on March 19th,that"We're getting Britain building".Sadly,given the huge exlenl of Britain's housing shortage,the chancellor's proposed interventions do not add up to much.The biggest announcement was that the government will extend Help to Buy,a scheme that guarantees mortgages for people purchasing newly built homes.Mr Osbome also hopes to build a new town at Ebbsfleet,a patch of post-industrial land in the Thames estuary,and promises to speed up the redevelopment of several rotting 1960s and 1970s social housing estates in London.By making it easier for house builders to shift their stock,Help to Buy has probably helped boost building slightly,especially in northern cities where construction had all but ceased.Extending the programme will boost Britain's housing stock by 120,000 by 2020,the Treasury cltums,though it will also expose taxpayers to any future house-price crash.Mr Osborne also announced a new fund to support lending io smaU house builders-who have sLruggled to get financing in recent years which ought to have a similar effect.The new town is more advencurous.Ebbsfleei.where a high-speed rail link to London opened in 2007,has had plans for new homes for almost 20 years.Few have been built,mosdy because the site is a partially flooded quarry with little in the way of shops.public transport or infrastructure.The government's new idea is to create a development corporation with control over planning and the ability to borrow to clean up and prepare the site.That was how post-war new towns such as Milton Keynes and Stevenage were built.A sinular interventionism is visible in the plan to rebuild 1960s estates.Many of these,such as the Aylesbury Estate in SouLhwark and Robin Hood Gardens in Tower Hamlets,are crummbling.By increasing the density on the sites,and using the proceeds of selling the extra houses built,it ought to be possible to cover the cost of reconstniclion.Bui counciLs have been short of money to do much themselves,and private developers extract high retums in exchange for putting up capital.With central-govemment money,those projects ought to move quicker and councils ought to get more for their land. Ebbsfleet is mentioned in the text to show____
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D.the importance of building infrastructure