If $A$ and $B$ are coefficient of $x^n$ in the expansion of $(1+x)^{2n}$ and $(1+x)^{2n-1}$ respectively then $A/B$ equals

Question

$\begin{array}{1 1}(A)\;1\\(B)\;2\\(C)\;\large\frac{1}{2}\\(D)\;\large\frac{1}{n}\end{array}$