【正确答案】通常猪流感不会感染人类。美国历史上，每一两年在接触活猪的人群里会有一例感染。但从2005年12月到2009年1月间，人类感染猪流感病例上升了，这段期间出现12例病例。其中11例的病患有直接或间接活猪接触史；世卫组织官员正密切关注其发展。

【答案解析】[听力原文]
Normally, swine flu bugs don't infect people. Historically, there's a case every year or two in the U.S. among people who have contact with live pigs. But from December 2005 to January 2009 there was an uptick in swine flu cases. There were 12 human swine flu infections during this time. Eleven of these people had direct or indirect contact with pigs, and that has world health officials keeping a close eye on it.