is a growing world problem and nowadays the United Nations and its member countries hard

问题补充：

is a growing world problem, and nowadays the United Nations and its member countries hard to deal with it．

A. Desertification; are working

B. Desertified ; worked

C. Desert; work

D. Desertification; have worked

答案：

(答案→)A. Desertification; are working

B. Desertified ; worked

C. Desert; work

D. Desertification; have worked

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。