Answer: Option A
:
A
Lets first of all think about the situation given to us. Two parallel incident rays give us two parallel reflected rays. It means that at both the points the normal must be parallel, only then this is possible. (Think from the point of view of the law of reflection followed by both the rays.)
Now, we know that, for a spherical mirror, the normal at any point passes through the center of curvature. So, if all the normals pass through a point, they are not parallel.
So, we can only have parallel normal in the case of a plane mirror. So our mirror here is a plane mirror.