题目内容：
根据下面材料，回答题。 The world’S environment is surprisingly healthy．Discuss．If there were an examination topic，most students would tear it apart，offering a long list of complaints from local smog(烟雾)to glob-al climate change，from the felling(砍伐)of forests to the extinction of species．rnle list would largely be accurate，the concern legitimate．61)Yet the students who should be given the highest marks would actually be those who agreed with the statement．The surprise is how good things are，not how bad．
After all，the world’S population has more than tripled dunng this century，and world outputhas risen hugely，SO you would expect the earth itself to have been affected．Indeed，if people lived，consumed and produced things in the same way as they did in 1900(or 1950，or indeed 1980)，the world by now would be a pretty disgusting place，smelly，dirty，toxic and dangerous．
But they don’t．62)The reasons why they don't,and why the environment has not been ruined,have to do with prices 2 technological innovation,social change and government regulation in re-sponse to popular pressure．That is why today’s environmental problems in the poor countries ought，in principle，to be solvable．Raw materials have not run out，and show no sign of doing S0．
Logically，one day they must：the planet is a finite place．Yet it is also very big，and man is very ingenious．63)What has happened is that every time a material seems to be running short,the price has risen and,in response,people have looked for new sources of supply,tried to find ways to use less of the material,or looked for a new substitute．
For this reason prices for energy and for minerals have fallen in real terms during the century．The same is true for food．64)Prices fluctuate,in response to harvests,natural disasters and politi-cal instability；and when they rise,it takes some time before new sources of supply become availa-ble．But they always do，assisted by new farming and crop technology．The long term fiend has been downwards．
65)It is where prices and markets do not operate properly that this beningn (良性的)trend be-gins to stumble,and the genuine problems arise．Markets cannot always keep the environment healthy．If no one owns the resource concerned，no one has an interest in conserving it or fostering it：fish is the best example of this．
第61题答案为____________________
参考答案：
答案解析：