Consider the following: Which combination is correct (for $a, b > 0,\, r, s \in Q$)?

1. $a^r \cdot a^s = a^{r+s}$
2. $(a^r)^s = a^{rs}$
3. $(ab)^r = a^r \cdot b^r$

• ai and ii
• bii and iii
• ci and iii
• di, ii and iii