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
网友回答
A. had not been heard of
(答案→)B. has not been heard of
C. had not heard of
D. has not heard of
解析：C、D是主动语态，hear of表示“听说”，后面应该有宾语。前句意思是“他妹妹1998年离开的家”，说明1998年前有音信，由此可判断下句意思是“她妹妹从1998年到现在以来才没有音信的（被听说过）”，因此是现在完成时态。