$\tan^{-1} x + \cot^{-1} (x+1)$ is equal to :

Question

( A ) $\cot^{-1} (x^2 + x + 1)$
( B ) $\tan^{-1} (x^2 + x)$
( C ) $\tan^{-1}(x^2 + x +1)$
( D ) $cot^{-1} (x^2+x)$