题目

在四边形ABCD中，O是对角线的交点，下列条件能判定这个四边形为正方形的是（  ）     A．AC=BD，AB∥CD，AB=CD    B．AD∥BC，∠A=∠C     C．OA=OB=OC=OD，AC⊥BD     D．AO=CO，BO=DO，AB=BC 答案：CMary didn't go to John's birthday party because she ______. [     ]A. wasn't invited B. didn't invite C. isn't invited