Which one of the following statements correctly explains why vertical inversion is NOT observed in images formed by a plane mirror?
a) The brain turns the upside-down mirror image right-side up, so we do not notice vertical inversion.
b) Gravity keeps the image oriented the same way vertically, preventing the head and feet from swapping.
c) A plane mirror reverses the image sideways but not top–bottom.
d) Only a concave mirror can flip an image top–bottom; a plane mirror therefore shows no vertical inversion.