$\overrightarrow{r}=s\overrightarrow{i}+t\overrightarrow{j}$ is the equation of

Question

$$\begin{array}{1 1}(1) a\; straight \;line\; joining\; the\; points \overrightarrow{i} and \overrightarrow{j}&(2)x\;o\;y \;plane\\(3)y\;o\;z\;plane&(4)z\;o\;x\;plane\end{array}$$