A block is moving down a smooth inclined plane starting from rest at time t=0. Let Sⁿ be the distance travelled by the block in the interval t=n−1 to t=n. The ratio Sⁿ/Sn+1 is
a. 2n−1/2n
b. 2n−1/2n+1
c. 2n+1/2n−1
d. 2n/2n−1