b; each vertical line and horizontal line contain two right-side-up pairs of lightning bolts and one inverted pair. Each line contains a black, a white, and a gray central oval. Each line contains two gray cages and one white wire cage over the oval. Finally each line contains one image with two buttons, one with a single button, and one with no buttons. The missing image should have a pair of right-side-up lightning bolts and a white central oval with a gray cage, and one button.