题目

— Could you tell me what he said just now?   — Sorry, I_____ what was happening outside.    A. had thought                   B. was thinking         C. thought                D. think 答案：B如图，圆内接四边形ABCD的两组对边延长线分别交于E、F，∠AEB、∠AFD的平分线交于P点．求证：PE⊥PF．