SummarizationRead each of the following short paragraphs and complete the the phrase or sentence that expresses the main idea of the paragraph.The first letter of the missing word is given be fore the blank. Paragraph 1.In the U, S., cases of polio are now extremely rare, and ironically, are almost always caused by the Sabin vaccine itself —being live, the virus can mutate to a stronger form. Elsewhere there are still about 250,000 cases per year, mostly in developing nations where vaccination has not become widespread. The World Health Organization has goals to eradicate polio completely in the first decade of the twenty-first century.1. The d______of polio.
【正确答案】：distribution
【题目解析】：P267
