The world’s cities are getting more and more crowded. Cities such as Tokyo and Shanghai     1    (consider) “mega-cities”, because    2    their big size and huge populations.There are two main reasons why cities are becoming so crowded.

First, the primary cause of cities    3     (become) so crowded is economic. As a country develops, its cities become the engines of development, thus jobs are available in these areas. For example, Tokyo was the motor for Japan’s economic boom in the 1960’s and 70’s; as     4    result, its population increased    5     (rapid). People moved to Tokyo because they could find employment there.

Second, another    6     (contribute) factor is sociocultural. Thousands of people move to the cities not only for jobs but also for educational and personal reasons. The better universities in big cities attract thousands of students every year, and most of them choose     7    （work）in the city after graduation. Moreover, young people will move to the city as the rural areas are more    8     (tradition). Therefore, young people believe this is a barrier to their personal freedom.

In    9     (conclude), economic and cultural factors are the major causes of huge urban population. People will always move to the areas    10    provide opportunity and freedom.