A square sheet is folded left onto right and then top onto bottom. One hole is punched on the upright folded edge and another in the open part. Which figure shows the opened sheet?

Undo the top-bottom fold: each hole gets a twin in the top half. Undo the left-right fold: the two holes on the upright crease stay single (they sit on the centre line), while the other two get twins on the left. Six holes: (b).