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参考解析：
刷刷题刷刷变学霸
举一反三
【单选题】Animal studies are under way, human trial protocols are taking shape and drug makers are on alert. All the international health community needs now is a human vaccine for the bird flu pandemic sweepin...
A.
it has strong side effect to the elderly.
B.
it may turn ineffective in a short period.
C.
it is useless in preventing the virus.
D.
it hasn’t been tested in humans.
【单选题】在客运结构的影响因素中，决定客运结构首要条件的是（）。
A.
各种运输方式的运行速度
B.
运输方式服务质量
C.
国家的经济政策和运输政策
D.
国家经济发展水平和阶段