$\sqcap_{n=2}^{\infty}\;\large\frac{n^3-1}{n^3+1}$ equals

Question

$(a)\;\large\frac{1}{3}\qquad(b)\;\large\frac{2}{3}\qquad(c)\;\large\frac{2}{7}\qquad(d)\;\large\frac{1}{10}$