选择国家下拉选,在省份下拉选中填充所有这个国家的省,再选择省,在城市下拉选中填充所有该国家,该省的所有城市的三级联

Select the country drop-down, fill all provinces in the province drop-down, select the province, fill all the countries in the city drop-down, three cascades of all cities in the province