Drawing 120º Without a Protractor

Q. John draws line segment AB, then with A as the center and AB as the radius, he draws a semicircle. Taking the same radius and with B as the center, he draws another two arcs intersecting the semi-circle at the points C and D. What is the measure of $\angle$CAD?

1. ${60}^{\circ }$
2. ${150}^{\circ }$
3. ${90}^{\circ }$
4. ${120}^{\circ }$