The correct option is D Principal axis
We know that,
Pole :- is the midpoint of the aperture of the spherical mirror.
Radius of curvature :- is the radius of the sphere of which the spherical mirror is made.
Principal axis :- is the line joining centre of curvature and pole.
Focus :- is the point where rays from infinity converge after reflection from a concave mirror or seem to diverge after reflection from a convex mirror. This point depends on the rays' closeness to the principal axis.
So, pole, radius of curvature and principal axis depend on the geometry of the mirror. Focus depends on the closeness of rays to the principal axis i.e whether they are paraxial or not.