All four corners of a paper square are folded in to the centre, and the diamond is then folded top half down. A triangle pointing up and a round hole are punched. Which figure shows the opened square?

Undo the half fold: twins in the top half, the triangle now pointing down. Undo the corner folds: each hole lies on a corner flap, so each gets one more twin out in that corner; a slanting crease turns up into left and down into left as well: (a).