Influenza has been with us a long time. According (51) some Greek writers on medical history, the outbreak of 412 B.C. was of influenz
a. The same has been suggested of the sickness that swept through the Greek army (52) Syracuse in 395B.C. Flu is a disease that moves most quickly among people (53) in crowded conditions, hence, it is likely to attack armies. During the nineteenth century there were five widespread (54) of influenza. The last of the five (55) in 1889 and marked the beginning of the story of influenza in our time. Like the (56) started in Asia. For more than forty years before that outbreak, influenza had steadily (57) and was believed to be dying out. A new group of outbreaks was introduced by the great outbreak of 1889-1890 and for the next quarter of a century flu (58) a constant threat. In April 1918 flu broke out among American troops stationed in France. It quickly spread through all the armies but caused relatively (59) deaths. Four months later, (60) , a second outbreak started which proved to be a killer. It killed not only the old and already sick but also (61) young adults. It went through every country in the world, only a few distant islands in the South Atlantic and the Pacific remaining (62) . It brought the life of whole countries (63) , food supplies stopped and work loss was very great. Before the great outbreak ended, it (64) at least 15 million people. Thereafter there have been several great outbreaks throughout the world. It is thus (65) that influenza is a terrible infection that we have to pay more attention to.
【答案解析】[解析] 上面说到，“这五次大爆发的最后一次出现于1889年……像最近一次大爆发一样，它起源于亚洲”，此空白处从语法上分析，应该是一个能够代替那次爆发的主语，it是最恰当的；用which就不恰当，因为这里不可能是一个非限制性定语从句，况且which是指the recent outbreak还是指the last of the five也不明确，因此绝对不能用which。