______the library for hours without finding anything useful, I turned to my prof

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问题 ______the library for hours without finding anything useful, I turned to my professor for help.

选项 A、To search
B、Having searched
C、Have searched
D、Searching

答案 B

解析考查现在分词的完成时。表示其动作在谓语动词的动作之前完成，作时间或原因状语，找资料是发生在寻求帮助之前，用having seacrched，故选B。

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