题目内容：
根据下列材料请回答题：sustainable development is applied to just about everything from energy to clean water and economic growth,and as a result it has become difficult to question either the basic assumptions behind it or the way the concept is put to use.this is especially true in agriculture,where sustainable development is often taken as the sole measure of progress without a proper appreciation of histrorcal and cultural perspectives.
To start with,it is important to remember that the nature of agriculture has changed markedly throughout history,and will continue to do so .medieval agriculture in northern Europe fed,clothed and shelered a predominantly rural society with a much lower population density than it is today.it had minimal effect on biodiversity,and any pollution it caused was typically localized.in termsof energy use and the nutrients captured in the product it was relatively inefficient.
Contrast this with farming since the start of the industrial revolution.competion from overseas led farmers to specialize and increase yields.throughout this period food became cheaper,safe and more reliable.however,these changes have alsoled to habitat loss and to diminishing biodiversity.
What’smore,demand for animal products in developing countrics is growing so fast that meeting it will require an extra 300 million tons of grain a year by 2050.yet the growth of cities and in dustry is reducing the amount of water available for agriculture in many regions.
All this means that agriculture in the 21st century will have to be very different from how it was in the 20th.this will require radical thinking.for example,we need to move away from the idea that traditional practices are inevitably more sustainable than new ones.we also need to abandon the notion that agriculture can be “zero impact”. The key will be to abandon the rather simple and static measures of sustainability,which centre on the need to maintain production without increasing damage.instead we need a more dynamic interpretation,one that looks at the pros and cons of all the various way land is used.there are many different ways to measure agricultural performance besides food yield:energy use, environmental costs,water purity,carbon footprint and biodiversity. It is clear, for example,that the carbon of transporting tomatoes from spain to the UK
Is less than that of producing them in the UK with additional heating and lighting.but we do not know whether lower carbon footprints will always be better for biodiversity.
What is crucial is recognizing that sustainable agriculture is not just about sustainable food production.
How do people ofen measure progress in agriculture?
A．By its productivity
C．By its impact on the environmet
B．By its sustainability
D．By its contribution to economic growth
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