Nobody really knows how big Lagos is. What’s indisputable is that it’s growing very quickly. Between now and 2050, the urban population of Africa could triple. Yet cities in sub-Saharan Africa are not getting richer the way cities in the rest of the world have. Most urban Africans live in slum (贫民窟); migrants are often not much better off than they were in the countryside. Why?

    The immediate problem is poverty. Most of Africa is urbanizing at a lower level of income than other regions of the world did. That means there’s little money around for investment that would make cities liveable and more productive. Without upgrades and new capacity, bridges, roads and power systems are unable to cope with expanding populations. With the exception of South Africa, the only light rail metro system in sub-Saharan Africa is in Addis Ababa, Ethiopia. Traffic jam leads to expense and unpredictability, things that keep investors away.

In other parts of the world, increasing agricultural productivity and industrialization went together. More productive farmers meant there was a surplus that could feed cities; in turn, that created a pool of labour for factories. But African cities are different. They are too often built around consuming natural resources. Government is concentrated in capitals, so is the money. Most urban Africans work for a small minority of the rich, who tend to be involved in either cronyish (有裙带关系的) businesses or politics. Since African agriculture is still broadly unproductive, food is imported, consuming a portion of revenue.

    So what can be done? Though African counties are poor, not all African cities are. In Lagos, foreign oil workers can pay as much as $65,000 per year in rent for a modest apartment in a safe part of town. If that income were better taxed, it might provide the revenue for better infrastructure. If city leaders were more accountable to their residents, they might favour projects designed to help them more. Yet even as new roads are built, new people arrive. When a city’s population grows by 5% a year, it is difficult to keep up.

49. C) They have developed at the expense of nature.

解析：首先在题目中找到定位词African cities are different，然后回原文定位至第3段第3句。下文提到，非洲城市往往是在消耗自然资源的基础上建立起来的。最后看选项：A) 吸引大量的农民劳动力。该段第2句提到农民的生产力水平更高反过来为工厂创造了大量的劳动力，但该句形容的是其他地区的城市，并不是指非洲的城市，故排除。B) 过度依附于农业生产力。该段尾句提到非洲生产力普遍低下，食品需要进口，这就意味着非洲没办法依靠工业生产力，故排除。C) 发展以牺牲自然资源为代价。符合原文信息，故正确。D)过度依靠外国投资。该段尾句提到投资人因为交通不便对非洲望而却步，故排除。