Find the middle term in the expansion of $(3x-\large\frac{x^3}{6})^9$

Question

$\begin{array}{1 1}(A)\;\large\frac{189}{8}\normalsize x^{17};-\large\frac{21}{16}\normalsize x^{19}\\(B)\;\large\frac{189}{8}\normalsize x^{17};-\large\frac{22}{16}\normalsize x^{15}\\(C)\;\large\frac{8}{189}\normalsize x^{17};-\large\frac{21}{16}\normalsize x^{19}\\(D)\;\large\frac{8}{189}\normalsize x^{17};-\large\frac{25}{4}\normalsize x^{13}\end{array} $