One of the key challenges in urban architecture over the next 50 years will be figuring out how to squeeze vast numbers of additional people into urban areas that are already extremely crowded. London, for example, will somehow have to deal with a projected 100,000 extra inhabitants every year until 2016. The current plan of building a new “satellite towns” of the city causes a lot of problems---but architecture think tanks are working on ambitious solutions that go vertical instead of horizontal in search of space. In terms of population density, London is one of the least crowded major cities in the world---four times fewer people per square kilometer than Paris, for example, six times fewer than New York and eight times fewer than Cairo. But the fact remains that the city’s population is growing at a rapid rate, and horizontal expansion into the surrounding areas is eating up increasingly important agricultural land, as well as worsening all the transport problems that come with urban growth. Popular Architecture would propose a radically different solution. The proposal is to go upwards, with vertical towers of considerable size, each representing an entire new town, by the time it’s completed. Each tower would be 1500 meters high. Beyond mere accommodation, each tower would function as an entire town unit, with its own schools, hospitals, parks and gardens, sports faculties, business areas and community spaces. The population density of such a tower could help lower the individual energy requirements of each inhabitant, reducing the ecological impact of the population as a whole. The village towers are considered as hollow tubes, with large holes to allow light and air though the entire construction. Occasional floor discs spread throughout the height of the building will give inhabitants large central areas in the middle of the tube to use as gathering spaces. While the building itself is unlikely ever to be seriously considered for construction---imagine the number of elevators it would need, let alone the safety implications of open areas at such heights and with such wind exposure---the concept can serve as conversation-starter for urban planners looking to face the challenges of the current and coming countries. One key challenging task for urban architects in the future is to ______. A.build new satellite towns B.work out ambitious plans C.design less crowded cities D.accommodate more inhabitants Which of the following cities has the largest population density？ A.Cairo. B.Paris. C.London. D.New York. Horizontal expansion not only wastes land, but makes it hard for London to ______. A.handle its safety problems B.resolve its transport issues C.control its population growth D.measure its population density The vertical tower would represent an entire new town in itself because______. A.it is energy-saving B.it is cost-effective C.it is self-sufficient D.it is comfort-oriented For city planners today, the idea of building a vertical tower can become______.A.a topic for fun B.a shocking reality C.a modest proposal D.a source of inspiration