A boy stands in various distances in front of a mirror; his image remains erect at all times. It has to be a mirror.

 

A plane mirror's image is always formed behind the mirror, hence it can't be captured on a screen. As a result, they produce fictitious and erect images.

Convex mirror: The nature of the image produced by a convex mirror is unaffected by the distance between the item and the mirror. The images are always imaginary, a fraction of the size of the object, and hidden behind the mirror.

Hence option (D) is correct.