Which figure shows the opened sheet when a square sheet is folded along one diagonal, then along the other, the small triangle is folded in half once more, and the two shaded pieces are cut away?

Unfold in reverse: mirror the cuts in the last crease, then in the second diagonal, then in the first. The notch on the outer edge turns up twice on every side of the sheet, and the cut on the folded edge opens into diamonds on both centre lines, all in an 8-fold pattern: (d).