The distance of the point $(1,1,1)$ from the plane passing through the points $(2,1,1),\:(1,2,1)\:and\:(1,1,2)$ is ?

Question

$\large(a)\:\frac{1}{\sqrt 3}\:\:\:\qquad\:\:(b)\:\:1\:\:\:\qquad\:\:(c)\:\:\sqrt 3\:\:\:\qquad\:\:(d)\:\:2$