In B the upper half of A is completed in a certain way. Complete C in the same way and choose the answer.

B keeps A's top half and adds its reflection in the flat middle line, as if the middle line were the surface of water: the arrow pointing up-right gets a copy below pointing down-right, and the dot gets a copy near the bottom. Doing this to C gives a flag with an upside-down copy below it and a star with a copy below it: (d). (a) uses an upright mirror, (b) a half turn and (c) moves the top half instead of copying it.