_________ is a growing world problem, and nowadays the United Nations and its member countries _________hard to deal with it．A.Desertification; are workingB.Desertified ; workedC.Desert; workD.Desertification; have worked
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A解析第一空填：Desertification“沙漠化”，第二空考时态：句意是：沙漠化是日益严重的世界问题，现在联合国和成员国正努力对付它。用现在进行时，选A。