$\begin{array}{1 1} \pm \large\frac{\overrightarrow{i}+\overrightarrow{j}-2 \overrightarrow{k}}{6} \\ \pm \large\frac{\overrightarrow{i}+\overrightarrow{j}- \overrightarrow{k}}{\sqrt 3} \\ \pm \large\frac{\overrightarrow{i}+\overrightarrow{j}+ \overrightarrow{k}}{\sqrt 3} \\ \pm \overrightarrow{k} \end{array} $