Given a semicircle with $\text{O}$ as the centre, as shown in the figure, the ratio $\frac{\overline{AC}+\overline{CB}}{\overline{AB}}$ is _______, where $\overline{AC}$, $\overline{CB}$ and $\overline{AB}$ are chords.
1. $\sqrt{2}$
2. $\sqrt{3}$
3. $2$
4. $3$