Vector Algebra

If $\vec{a}=\left(\begin{array}{c}2\\ -5\\ 8\end{array}\right)$, $\vec{b}=\left(\begin{array}{c}1\\ -3\\ -7\end{array}\right)$ and $\vec{c}=\left(\begin{array}{c}-3\\ 2\\ -1\end{array}\right)$, then the unit vector(s) parallel to $\vec{a}+\vec{b}+\vec{c}$ is(are)