[填空题]Since the beginning of human evolution, men have migrated（迁移）across continents in search of food, shelter, safety, and comfortable weather. People still move for these reasons, but new reasons for human migration are arising, such as job relocation(重新安置) and overpopulation. Three million migrants are moving from poor countries to wealthier ones each year, and increasingly, their destination is a neighboring country in developing parts of the world. People are moving within the developing world for the same reasons as they migrate to wealthier nations. People from poor countries are going to less poor countries, fleeing wars and conflicts. They are also responding to population pressures because some countries are densely populated, and they often have high population growth. Those people need to go somewhere else. There are three main reasons why people move. The basic categories and percentages are as follows, according to the Current Population Surveys (CPS): Family-re