If vectors a_1 =x i - j + k and a_2 = i +y j +z k are collinear, then a possible unit vector parallel to the vector x i +y j +z k is:

If vectors $\displaystyle \overrightarrow{a_1}=x \hat{i}-\hat{j}+\hat{k}$ and $\displaystyle \overrightarrow{a_2}=\hat{i}+y \hat{j}+z \hat{k}$ are collinear, then a possible unit vector parallel to the vector $\displaystyle x \hat{i}+y \hat{j}+z \hat{k}$ is :