Publicising his imminent new series about the evolution of animals, Sir David Attenborough said this week that he thought a redu

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问题     Publicising his imminent new series about the evolution of animals, Sir David Attenborough said this week that he thought a reduction in human population in this century is impossible and "we’re lucky to be living when we are, because things are going to get worse". People will look back in another 100 years "at a world that was less crowded, full of natural wonders, and healthier". His is a common view and one I used to share. He longs for people to enjoy the open spaces and abundant herds of game that he has been fortunate enough to see. To that end he thinks it vital that there should be fewer of us. I would now disagree with his two premises. It’s actually quite likely, rather than impossible, that population will be falling by the end of this century and that the people alive then will have lots more wilderness to explore and wildlife to admire than today.
    The rate at which world population grows has roughly halved from 2 per cent a year in the 1960s to roughly 1per cent a year now. Even the total number of people added to the annual population has been dropping for nearly 30 years. If those declines continue, they will hit zero in about 2070. In recent decades the birth rate has fallen in every part of the world. Fertility in Bangladesh has fallen from nearly 7 children per woman in the 1960s to just over 2 today; Kenya from 8 to 4. 5; Brazil 5. 7 to 1. 8; Ireland 3. 9 to 2.
    It is still conventional wisdom that the only way to get population growth down is to be nasty to people, albeit with noble motives. You must coerce, bribe, shame or educate them into having fewer babies against their preferences. China did indeed bring down its birth rate with one-child policy. India tried to introduce coerced sterilization in the 1960s in return for food aid from America, but was defeated by popular protest and democracy.
    Yet everywhere else voluntary birth control proved a more effective weapon than coercion, and the birth rate came down just as fast. This was because nice things happened: economic growth, female emancipation and, above all, the conquest of child mortality. So long as women have some access to the means of birth control, then one of the best predictors of a falling birth rate is a falling child mortality rate. Once they think their kids will survive, they start investing in them, rather than in having more kids. You can see this in the statistics. There is no country on Earth with a child mortality rate below 10 per 1,000 births that has a fertility higher than 3 children per woman; whereas all countries except one(Swaziland)that have a child mortality rate above 100 also have a fertility rate above 4. 5. Keep kids alive and you bring down population growth.
    Which is why the recent plummeting of child mortality in Africa is such good news for Sir David and others with his concerns. Thanks to rapid economic growth, better governance and much improved public health, most African countries are now experiencing child-mortality falls of 5 per cent or more a year. These falls will surely soon be followed, as night follows day, by an even faster fall in birth rates. Europe, Asia and Latin America have already gone through this transition and most countries are producing babies at or below replacement rate of 2. 2 per woman, at which population stabilizes. Africa is following suit almost exactly.
    For this reason alone, I suspect the world population will stop growing and begin to shrink even earlier than 2070. But even if it does not, there is good reason to reassure Sir David that our great grandchildren will have more wildlife to look at than he has had. An ingenious study by Rockefeller University scientists has recently calculated that even with population continuing to grow, we have almost certainly already passed "peak farmland", because of the rate at which fertilisers are improving yields. We will feed nine or ten billion people in 2070 from a considerably smaller acreage than we need to feed seven billion today.
    Land sparing is already occurring on a grand scale. Forest cover is increasing in many parts of the world, from Scotland to Bangladesh. Wildlife populations are booming in Europe, in the polar regions and North America and this is happening fastest in the richest countries. According to one recent report, animal populations grew by 6 % in Europe, North America and Northern Asia between 1970 and 2012, while shrinking in tropical regions. There is almost a perfect correlation between the severity of conservation problems and poverty, because the richer people get, the less they try to live off the land and compete with nature—the less they seek bushmeat and charcoal from the forest.
    Once again, Africa may spring a pleasant surprise. Over the decades agricultural yields in Africa hardly budged while they doubled or quadrupled in most of Asia. That is entirely down to a dearth of fertilizer and it is beginning to change. If African yields were to rise, the acreage devoted to farmland globally would start to fall even faster, releasing more and more land for "rewilding". The great herds and flocks that so delight Sir David would reassemble in more and more places. The happy conclusion is that making people better off and making nature better off are not in opposition; they go hand in hand.
The author uses the expression "as night follows day"(para. 5)______.

选项 A、to show that human population growth is governed by the natural law
B、to explain that fall in birth rates will inevitably follow child-mortality falls
C、to argue that there is no reason to feel pessimistic about human population growth
D、to convince us that social progress leads to more effective birth control

答案B

解析
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