Let `T ,` be the `r` th term of an AP, for `r=1,2,3dot` if for some positive integers `m , n` we have `T_m=1/n` and `T_n=1/m ,` then `T_(m n)` equals (1998, 2M) `1/(m n)` (b) `1/m+1/n` 1 (d) 0