题目

His sister left home in 1998, and ____ since. A. had not been heard of  B. has not been heard of   C. had not heard of       D. has not heard of   答案：B句意: 他妹妹在1998年离开家, 从那以后就没了音讯。根据句意, 指的是过去离开以后, 到现在一直没音讯, 故用现在完成时; hear of与his sister在本句中为被动关系, 故用被动语态, 所以选B。  11、如图，CE⊥AB于点E，BD⊥AC于点D，BD、CE交于点O，且AO平分∠BAC，则图中的全等三角形共有4对．