ABC + DEF = 1111, wherein A, B, C, D, E, and F are distinct non-zero digits.

We may get a resultant of 1111 if: $C + F = 11$, say $2 + 9 = 11$ $B + E = 10$, say $3 + 7 = 10$ $A + D = 10$, say $4 + 6 = 10$

We can double check this by adding $432 + 679 = 1111$

So, $A + B + C + D + E + F = 4 + 3 + 2 + 6 + 7 + 9 = 31$

Hence, option (D) is correct.