Due to the high housing prices and prices in China's large cities, the cost of living is significantly higher than that of small and medium cities, especially for small towns, the cost of living in large cities is several times that of small towns. In this way, it is bound to limit the rural population Influx of large cities. Therefore, China's only reliance on the development of large cities to achieve urbanization is an unsustainable and difficult road. Which of the following is the premise implicit in the above argument? ['There is no upper limit on the capacity of large cities to absorb the rural population.', 'All towns are fully developed before they can be called urbanized.', 'Large cities are far more attractive to the rural population than small and medium cities.', 'To achieve urbanization, cities need to fully absorb the rural population.']