Counting odd days from 2025 until they total 7 (i.e. 0): 2025 -> 1, 2026 -> 1, 2027 -> 1, 2028 (leap) -> 2, 2029 -> 1, 2030 -> 1, giving a total of 7 odd days. Hence the calendar for 2031 is the same as that of 2025. (A non-leap year calendar repeats after 6 or 11 years; of the options only 2031 fits.)