Three flags, each of different colour, are available for a military exercise. Using these flags, different codes can be generated by waving i) a single flag of different colours, or ii) any two flags in a different sequence of colours, or iii) three flags in a different sequence of colours. The maximum number of codes that can be generated is

1. (a)6
2. (b)9
3. (c)15
4. (d)18