Let the points $A ( 0,0,0 )$ and $B ( 1,1,1 )$, and the line $r \equiv ( x , y , z ) = ( \lambda , \lambda , \lambda + 1 ) , \lambda \in \mathbb { R }$. a) (1 point) Find an equation of the plane with respect to which the points $A$ and $B$ are symmetric. b) (1 point) Find an equation of the plane that contains the line $r$ and passes through the point $B$. c) (0.5 points) Find an equation of a line that is parallel to $r$ and passes through $A$.