A line passes through the point $(x_1,y_1,z_1)$ and is parallel to the vector $\langle a,b,c\rangle$. Its symmetric form is

If a line passes through $(x_1,y_1,z_1)$ and has direction ratios $(a,b,c)$, then its vector form is $\vec{r}=\vec{r_0}+\lambda\langle a,b,c\rangle$. Converting this to Cartesian symmetric form gives $\dfrac{x-x_1}{a}=\dfrac{y-y_1}{b}=\dfrac{z-z_1}{c}$. Option D is the equation of a plane, not a line.