For an AP with first term $a$ and common difference $d$, if $\large\frac{S_{nx}}{S_{x}}\:(S_{r}$ denotes sum upto $r$ term$)$ is independent of $x$ then,

Question

$(a)\;a=d\qquad(b)\;a=\large\frac{d}{2}\qquad(c)\;a=2d\qquad(d)\;None\;of\;these$