Fill in the Blanks Unit 14Online version This is a listening exercise for students preparing for ielts by John E 1 The world ? s population is , no more than in its cities . Today , there are 21 megacities , each containing more than 10 million inhabitants , three - quarters of them in nations . By 2020 , there are expected to be at least 27 megacities . Such a pressing rate of brings its own problems , especially in developing nations , where the majority of the megacities will be found . and educational opportunities are the main attraction of urban centers . But hopes for a better life are often dashed as overpopulation puts an strain on the infrastructure of the cities and their ability to provide basic necessities such as clean and a place to live . Many rural migrants fail to find work , and therefore cannot afford basic . In some megacities up to 50 per cent of the residents live in slums . This problem is , with the Nations predicting that half the world ? s population will be living in cities next year . If the infrastructure within those cities does not grow at the same rate the result will be .
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