63. (a) Virtual, since the image is formed by plane mirrors. (b) Same. One can easily verify this by locating, for example, the images of two points, one at the head of the penguin and the other at its feet. (c) Same, since the image formed by any plane mirror retains the original shape and size of an object. (d) The image of the penguin formed by the top mirror is located a distance D above the top mirror, or L + D above the bottom one. Therefore, the final image of the penguin, formed by the bottom mirror, is a distance L + D from the bottom mirror.