The mirror used in periscope is:A. Convex mirror.B. Concave mirror.C. Plane mirror.D. Any of the above can be used.

C. Plane mirror.

In a periscope, plane mirrors are typically used. A periscope is an optical instrument that allows the viewer to see objects that are not in their direct line of sight by using multiple reflections from plane mirrors to redirect the light path. It usually consists of two or more plane mirrors placed at specific angles to achieve the desired reflection and viewing angle.