Structural mobility refers to large-scale changes in the nature and distribution of the social environment, social class, and population caused by changes in production technology or social structure, often without the transfer of human will. Based on the above definition, which of the following is not a structural flow? ['with the rapid development of the eastern coastal economy, the population of the central and western regions has moved eastward.', 'due to a military coup in the country, a large number of citizens of a country have recently poured into neighboring countries.', 'dissatisfaction with the decline in the quality of life in first-tier cities, and the return of talents to second- and third-tier cities.', 'Urbanization is manifested by the transfer of rural population to cities and the continuous development and improvement of cities.']