D
You over lay each two images that are next to each other to produce the image on top
If two dots lay on each other they cancel each other so no dot same with circles if they lay on each others they cancel if not then it stays
D
You over lay each two images that are next to each other to produce the image on top
If two dots lay on each other they cancel each other so no dot same with circles if they lay on each others they cancel if not then it stays