If you have a shape and fold it into the back (and look at it from the back) it will look the same as if you are looking at it without folding it.
Think about it. Lets say you fold it into the page like you are saying. Now look at it from the FRONT (THROUGH the white block that would be in front). The dark figure would be in the orientation of the main dark figure in choice A... this orientation is not possible.
Basically, choice A is the mirror image...
Look at it for a while and think about it.
Is there a 3D explanation?
Maybe someone else can explain better...
