The equation of the plane through origin and the line of intersection of the planes $\overrightarrow r.\overrightarrow a=\lambda\:\:and\:\:\overrightarrow r.\overrightarrow b=\mu$ is ?

Question

$\begin{array}{1 1} (a)\:\overrightarrow r.(\lambda\overrightarrow a-\mu\overrightarrow b)=0\:\qquad\:(b)\:\overrightarrow r.(\lambda\overrightarrow b-\mu\overrightarrow a)=0\:\qquad\:(c)\:\overrightarrow r.(\lambda\overrightarrow a+\mu\overrightarrow b)=0\:\qquad\:(d)\:\overrightarrow r.(\lambda\overrightarrow b+\mu\overrightarrow a)=0 \end{array} $