By the end of last year we ___ each other for ten years.A.have known B.knew C.were learning D.had known
问题描述：
By the end of last year we ___ each other for ten years.
A.have known B.knew C.were learning D.had known
答
D
答
D last year已经是过去了 过去的过去用过去完成时
答
D.had known
By the end of last year 截止到去年底 BY加过去时间可以看做过去完成时的标志