The vector equation of the x-axis is given by

The vector equation of the $x$-axis is given by

A. $\overrightarrow{\mathrm{r}}=\hat{\mathrm{i}}$

B. $\vec{r}=\hat{j}+\hat{k}$

C. $\overrightarrow{\mathrm{r}}=\lambda \hat{\mathrm{i}}$

D. none of these