Let `T_r a n dS_r` be the rth term and sum up to rth term of a series, respectively. If for an odd number `n ,S_n=na n dT_n=(T_n-1)/(n^2),t h e nT_m` (`m` being even)is `2/(1+m^2)` b. `(2m^2)/(1+m^2)` c. `((m+1)^2)/(2+(m+1)^2)` d. `(2(m+1)^2)/(1+(m+1)^2)`