Which of the dice (a) to (d) can NOT be folded from the numbered net shown at the top?

The net gives the pairs 2–6, 4–1 and 5–3. All four dice avoid showing a pair together, so the order round the corner decides. (b) shows 6, 4 and 3 correctly; (c) shows the same three faces going round the other way, so (c) is a mirror image. (a), (b) and (d) can all be made.