A small block slides down on a smooth inclined plane, starting from rest at time `` t=0 . `` Let `` S_{n} `` be the distance travelled by the block in the interval `` t = n -1 `` to `` t = n . `` Then, the ratio `` \frac{ S _{ n }}{ S _{ n +1}} `` is :
(A) `` \frac{2 n-1}{2 n} ``
(B) `` \frac{2 n-1}{2 n+1} ``
(C) `` \frac{2 n+1}{2 n-1} ``
(D) `` \frac{2 n}{2n -1} ``