Within a couple of years, every country that started polio eradication rapidly eradicated all three of their polio viruses, with the exception of four countries that you see here.
几年之类 那些开始进行脊髓灰质炎根除的国家 迅速地消灭了现有的三种脊髓灰质炎病毒 唯一例外是图表上的这四个国家