Fold a square sheet along one diagonal into a triangle, then fold the triangle in half again along the dotted line, and punch two holes. Which figure shows the opened sheet?

Undo the second fold (mirror in the other diagonal) to get 4 holes, then undo the first fold (mirror in the first diagonal) to get 8 holes, symmetric about both diagonals: (c). (b) wrongly mirrors in the centre lines.