confidence and patience, they failed to settle the difficult problem.
A. Lack in
B. Lacking of
C. Lacking
D. Having lacked
网友回答
A. Lack in
B. Lacking of
(答案→)C. Lacking
D. Having lacked
解析：句意：因为缺乏自信，他们没能解决这个困难的问题。这里需要非谓语动词做状语，they和lack是主动关系，用现在分词做状语，排除A。B项如果接of，lack是名词，D项表示先后关心，这里没有，选C。