HN1 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
A.A.limited B.which C.crossing D.which
【参考答案】
C 解析:题干中出现的关键词H5N1特征性很强,可在第四段中找到。第一句话以及与其对应的上一段中的 cross ......