Write down the complete system of least non-negative residues of the following moduli:
(a) 6 (b) 12 (c) 17
(a) $\{ 0, 1, 2, 3, 4, 5 \}$
(b) $\{ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 \}$
(c) $\{ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 \}$