People have lived in cities for thousands of years. Yet even just 100 years ago, more people     1     (live) in the country than in cities. Today, with the population in the world     2     (increase) sharply, more people move to cities for various     3     (reason). For many it is for work or education. Some are     4     (simple) attracted to city life. By the year 2030, it is thought     5     more than sixty percent of the world's population will be living in cities. More and more cities will become megacities (特大城市), and they will     6     (find) in different parts of the world.

Maybe one megacity is not the same as another     7     they do have common problems, such as air     8     (pollute), housing problems, traffic jams and so on. Making these cities work well for every person living in them will be     9     great challenge in the future. However, we do believe when people work together, they can find solutions which will help make these megacities happy, healthy and     10     (excite) places to live in.