埃博拉疫情自2014年2月起至2015年3月10日止爆发1年多来，在几内亚、利比里亚与塞拉利昂3个疫情蔓延最为严重的国家，已经夺走1.4万条人命，确诊、疑似病例则高达24350多人．

埃 博拉出血热是由埃博拉病毒（Ebola virus）引起的一种烈性传染病．该病感染潜伏期从2天到21天不等．患者的最初症状是突然发烧、头痛，随后是呕吐、腹泻和肾功能障碍，最后是体内外大 出血而死亡．直接接触感染了埃博拉病毒的人或动物的血、尿、体液、排泄物、分泌物、呕吐物等就有可能被埃博拉病毒感染．

科学家对埃博拉疫苗的研究有所突破、疫苗进入临床试验阶段，在利比里亚蒙罗维亚，医护人员为首批招募的志愿者注射埃博拉疫苗，此后再逐步安排约2.7万人参与试验．根据以上材料，分析回答下列问题：

下列属于特异性免疫的是 （ ）

我国的植树节是几月几日。你还知道哪些节日？

    The American believe that anybody can become President of the United States. In a recent Hollyhood comedy(喜剧), that is exactly what happens.

    Dave Kovic, played by Kevin Kline, is a kind-hearted man who runs a business that finds people jobs. He leads a typical(典型的) American way of life, except for one thing— he looks exactly like the President, Bill Mitchell. In fact, the only thing that makes him different from the nation's leader is that he is very nice!

    The president has started using look-alikes during some public appearance. Dave is offered a chance to “serve his country” by becoming one. However, things go wrong. The President becomes very ill and Dave ends up acting as the President forever.

    Director Ivan Reitman, who made the popular and successful comedies like Twins, Ghostbusters and Legal Eagles, could have gone for easy laughs by making fun of the American government. Instead, Dave is an attractive comedy about an ordinary man in extraordinary situations. Kevin Kline gives a double performance as Dave and the President, and Sigourney Weaver is at her best as his First Lady. The love story that develops between her role and Dave is a real classic(经典).

    The film is 100% American. However, if you've ever felt that anybody could do a better job running the country than the people in power, then you'll enjoy Dave!