第34题: [单项选择]H5N1 is a flu strain ______. A. limited to Hong Kong B. which first affected human beings in 1961 C. crossing species barriers D. which was first isolated from American birds 参考答案:C 答案解析:细节题。
[定位] 题干中出现的关键词H5N1 特征性很强,在文中第四、五段出现过两次,需依次分析。
[解析] 根据第四段第一句话及与其对应的上一段中的cross species infectio