His sister left home in 1998, and _________ since.[ ]

A. had not heard of

B. has not heard of    

C. had not been heard of

D. has not been heard of

A：条件(1)充分，但条件(2)不充分．
B：条件(2)充分，但条件(1)不充分．
C：条件(1)和(2)单独都不充分，但条件(1)和条件(2)联合起来充分．
D：条件(1)充分，条件(2)也充分．
E：条件(1)和条件(2)单独都不充分，条件(1)和条件(2)联合起来也不充分．

点M(2，-3)的对称点M’(-2，3)．
(1)M和M’关于原点对称；(2)M和M’关于直线2x-3y=0对称．