题目

______ when to leave, I could only stay at home, _____ nothing.       A. Knowing not; done                                      B. Not having known; doing       C. Having not known; done                               D. Not knowing; doing 答案：D 解析: 略已知：如图，在四边形ABCD中，AB∥CD，对角线AC、BD相交于点O，BO=DO． 求证：四边形ABCD是平行四边形．