题目

 Is this the piano _______ your family for over eighty years?      A. belonged to       B. belongs to        C. belonged         D. belonging to 答案：D如图，⊙O是△ABC的外接圆，AC是直径，过点O作OD⊥AB于点D，延长DO交⊙O于点P，过点P作PE⊥AC于点E，作射线DE交BC的延长线于F点，连接PF．（1）求证：△ADO≌△PEO；（2）若∠OAD=30°，劣弧PC长为2π，求AC的长度．