How many of these four dotted nets would fold into a standard die, whose opposite faces always total 7?

(a): 1 and 6 are above and below the row, and the row 2 3 5 4 gives 2–5 and 3–4: all total 7. (b): the row ends give 2–5 and 3–4, the middles 1–6: all 7. (c): squares two steps apart on the staircase give 1–5, which totals 6, so it fails. (d): 3–4, 6–1 and 2–5: all 7. So 3 nets work.