If $f\left(\frac{3 x-4}{3 x+4}\right)=x+2$, then $\int f(x) d x$ is equal to
(A) $\operatorname{ex}-{ }^{2} \ln \left|\frac{3 x-4}{3 x+4}\right|+c$
(B) $-\frac{8}{3} \ln |x-1|+\frac{2}{3} x+c$
(C) $\frac{8}{3} \ln |x-1|+\frac{x}{3}+c$
(D) none of these