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  3. Over a century ago, Alfred Russell Wallace wrote that "we live in a zoologically poor world, from which all the hugest, fiercest

Over a century ago, Alfred Russell Wallace wrote that "we live in a zoologically poor world, from which all the hugest, fiercest

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问题     Over a century ago, Alfred Russell Wallace wrote that "we live in a zoologically poor world, from which all the hugest, fiercest and strangest forms have recently disappeared. " Researchers seeking to explain this " marvelous fact", as Wallace called it, fall into two camps, one invoking global climatic change and the other human hunting as the cause.

    Over the past few decades, the debate has become
    deadlocked, in part because most researchers have focused their attention on the Americas and northern Eurasia, where the extinction of the huge, fierce, and strange creatures, such as mammoths, and giant sloths(大树懒), occurred between 12, 500 and about 11, 000 years ago. This was a time of rapid climatic change, but it was also when humans first arrived in these regions, making it difficult to discern causality. Australia provides the only separate, continent-sized natural laboratory in which dramatic Quaternary extinctions occurred. It is thus of exceptional importance as a testing ground for extinction theories, but until now problems with dating have limited its potential. Miller and some people have now documented the extinction of the gigantic Australian bird and so have broken new ground in dating huge creatures extinction in Australia. At the same time, these authors have broken the current deadlock in the great huge creature extinction debate.
    It has long been appreciated that the intensity of Quaternary extinctions varied greatly around the world. In the oceans, Africa, and Southeast Asia, they were nonexistent or mild. Europe experienced moderate extinction rates, whereas the Americas, Australia, Madagascar, and many Oceanic islands suffered dramatic extinctions. North America lost 73% of all forms weighing more than 44 kg, but Australia suffered the most severely of all the continents, losing every terrestrial vertebrate(脊椎动物)species larger than a human, as well as many smaller mammals, reptiles, and flightless birds, the latter down to about a kilogram in weight. In all, about 60 vertebrate species were lost, including bizarre marsupials(有袋类动物)that resembled giant sloths, kangaroos, and a terrestrial horned tortoise that approached the size of a Volkswagen Beetle car. Establishing just when this bizarre array of creatures last trod Australia’s outback has been an intricate business, with many false leads and sites that are difficult to interpret.
    For decades, it was believed that the huge creatures survived until close to the time of the glacial maximum, some 20, 000 years ago, when temperatures were up to 9t cooler than at present and the continent was extremely arid. Conditions were so extreme that trees virtually disappeared from the inland, and 40% of Australia was transformed into a vast active dune field.
The difficulty in discerning the direct cause of the huge creatures’ extinction in______ has made the debate deadlocked.
选项
答案the Americas and northern Eurasia
解析 文中说这种争辩已陷于僵局，部分是因为大多数研究者将注意力集中于美洲和欧亚大陆的北部，那里，动物灭绝的时候也是人类首次涉足的时候，故导致动物灭绝的原因究竟是气候还是狩猎无法说清楚。根据介词in判断这里填地点。
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