$\triangle ABC$的内角$A$,$B$,$C$的对边分别为$a$,$b$,$c$,已知$9\sin^2B=4\sin^2A$,$\cos C=\dfrac{1}{4}$，则$\dfrac{c}{a}=$（ ）.
$\text{A.}$ $\dfrac{\sqrt{11}}{4}$
$\text{B.}$ $\dfrac{\sqrt{10}}{4}$
$\text{C.}$ $\dfrac{\sqrt{11}}{3}$
$\text{D.}$ $\dfrac{\sqrt{10}}{3}$