5. Given $f(x)=3 x^{2}-x+4$, $f(g(x))=3 x^{4}+18 x^{3}+50 x^{2}+69 x+48$.
Then, the sum of the coefficients of the integer polynomial function $g(x)$ is $(\quad$.
(A) 8
(B) 9
(C) 10
(D) 11
5.A.

Let the sum of the coefficients of $g(x)$ be $s$, then $f(g(1))=3 s^{2}-s+4=188$.
Solving for $s$ gives $s=8$ or $s=-\frac{23}{3}$ (discard).