The opened sheet at the top was folded left onto right and then top onto bottom, and ONE hole was punched. Which folded piece shows where the hole was punched?

The holes sit 2 units either side of the vertical centre line, and 1 unit either side of the horizontal centre line. On the folded quarter (bottom-right) that is 2 units right of the left fold and 1 unit below the top fold: (c). (a) swaps the two distances.