单选题 Some very rare drawings have been recovered for this exhibition through ______ research work in museums and libraries.
【正确答案】 C
【答案解析】句意：经过在博物馆和图书馆的苦心钻研，这次展览会上展出了一些极为罕见的画作。assiduous刻苦的；勤勉的；百折不挠的。minor较小的；不重要的；不严重的。