Question
No matter how far you stand from a certain mirror, your image always appears erect. What type(s) of mirror could this be?
Only a concave mirror
Only a convex mirror
Either a plane or a convex mirror
Only a plane mirror, never any curved mirror
Detailed Explanation
A plane mirror always gives an erect image, and a convex mirror also always gives an erect (virtual) image for any object position -- a concave mirror can give an inverted image for many positions, so it's excluded.