题目

如图所示，将△AOB绕着点O旋转180度得到△DOC，过点O的一条直线分别交BA、CD的延长线于点E、F，求证：AE=DF． 答案：【答案】证明见解析【解析】先利用旋转的性质得OB=OC，AB=CD，∠B=∠C，再证明△OBE≌△OCF得到BE=CF，从而可判断AE=DF．∵△AOB绕着点O旋转180度得到△DOC，∴OB=OC，AB=CD，∠B=∠C．在△OBE和△OCF中，∵，∴△OBE≌△OCF，∴BE=CF，∴BE﹣AB=CF﹣CD，即AE=DF．She is _____, but she looks young. [     ]A. in her fifty B. at her fifty C. in her fifties D. at her fifties