Let $z=a(\cos\large\frac{\pi}{5}$$+i\sin\large\frac{\pi}{5})$$\quad a\in R,|a| < 1$ then $S=z^{2015}+z^{2016}+z^{2017}+.......$ equals

Question

$\begin{array}{1 1}(A)\;\large\frac{a^{2015}}{z-1}&(B)\;\large\frac{a^{2015}}{1-z}\\(C)\;\large\frac{z^{2015}}{1-a}&(D)\;\large\frac{z^{2015}}{a-1}\end{array} $