题目内容：

Jack and Susan ________ each other since they were children,so nobody was surprised to hear that they were married.
A.knew B.have known C.had known D.were known

优质解答

C
since 一般和现在完成时连用,由于下文 so nobody was surprised to hear that they were married.是一般过去时,可见是相对这一过去时点来说的,过去的过去,用过去完成时