Concept:A ray passing through the centre of curvature of a concave mirror strikes the mirror normally.Explanation:The centre of curvature is the point whose distance from the mirror is the radius of curvature.A ray aimed at this point falls on the mirror along the normal to the surface.According to the law of reflection, the angle of reflection equals the angle of incidence.Since the ray is incident along the normal, both angles are 0∘.The reflected ray therefore travels back along the same path.Answer:A. 0∘