单选题 In an early survey conducted in 1888, a billion and a half people inhabited the earth. Now, the population exceeds seven billion. This means that the world must accommodate a new population roughly equal to that of the United States and Canada every three years! Even though the rate of growth has begun to slow down, most experts believe the population size will still pass eight billion soon.
If we examine the amount of land available for this ever-increasing population, we begin to see the problem. If everyone on the planet had an equal share of land, we would each have about 50,000 square metres. This figure seems to be quite encouraging until we examine the type of land we would have. Not all land is useful to humans as it cannot produce food. We can cut out about one fifth of it because it is permanently covered by snow and ice. Then we can cut out another one fifth because it is desert. Another fifth is too mountainous or is too great a height above sea-level. A tenth doesn"t have enough soil for crops to grow—it is bare rock.
Obviously, with so little land to support us, we should be taking great care not to reduce it further. But are we? We are consuming its "capital", which means its nonrenewable fossil fuels and other mineral deposits that took millions of years to form but which are now being destroyed in decades. We are doing the same with other vital resources not usually thought of as being nonrenewable such as fertile soils, groundwater and the millions of other species that share earth with us.
The birth of a baby in, for example, Hong Kong, imposes more than a hundred times the amount of stress on the world"s resources as a baby in India. Most people in India do not grow up to own cars or air-conditioners. Nor do they eat the huge amount of meat and fish that the Hong Kong child does. Their life-styles do not require vast quantities of minerals and energy. Also, they are aware of the requirements of the land around them and try to put something back into nature to replace what they take out.

【正确答案】 A

【答案解析】[解析] 细节题。根据文章第一段和第二段介绍现在地球上有超过70亿的人口，如果每个人在地球上都有一块相等大小的土地，则每个人可有50,000平方米的土地，所以地球一共有50,000×70亿平方米的土地。但是地球上不是所有地方都是可以居住的，因为有的土地不能产食物。有1/5被冰雪覆盖的不能生产食物，另外1/5是沙漠不能生产食物，还有1/5是高山，海拔过高也不能生产食物，还有1/10是裸岩，没有足够的土壤生长食物。所以每个人真正可以获得的生产食物的土地为[50,000×70亿×(1-1/5-1/5-1/5-1/10)]÷70亿，最后计算结果为A，故选A。