sustainable development is applied to just about eberything 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.

　　52. 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

　　53. Specialisation and the effort to incease yields have esulted in________.
　　A) Localised pollution C) competition from overseas
　　B) the shrinking of farmland D) the decrease of biodiversity

　　54.What does the author think of traditional farming practices?
　　A)They have remained the same over the centuries
　　B)They have not kept pace with population growth
　　C)They are not necessarily sustainable
　　D)They are environmentally friendly

　　55.What will agriculture be like in the 21st century
　　A) It will go through radical changes
　　B) It will supply more animal products
　　C) It will abandon traditional farming practices
　　D) It will cause zero damage to the environment

　　56 What is the author’s purpose in writing this passage?
　　A) To remind people of the need of sustainable development
　　B) To suggest ways of ensuring sustainable food production
　　C) To adance new criteria for measuring farming progress
　　D) To urge people to rethink what sustainable agriculture is