∵EF是AC的垂直平分线∴AE=CE,AO=CO,∠AOE=∠COF=90°∵AD∥BC∴∠DAC=∠BCA∵AO=CO,∠AOE=∠COF∴△AOE≌△COF(ASA)∴OE=OF∵AO=CO∴四边形AFCE是平行四边形∵AE=CE∴平行四边形AFCE是菱形
