9. Given real numbers $x, y$ satisfy $(2 x+y)^{3}+x^{3}+3 x+y=0$, then the value of $3 x+y$ is $(\quad)$.
A. -1
B. 0
C. 1
D. Uncertain
9. B. The given equation can be transformed into $(3 x+y)\left[(2 x+y)^{2}-x(2 x+y)+x^{2}+1\right]=0$,
$\because 2 x+y \in \mathbf{R}$, and $\Delta_{2 x+y}=x^{2}-4\left(x^{2}+1\right)=-3 x^{2}-10$, therefore $3 x+y=0$, hence the answer is B.