An interior designer is hanging a circular clock for a client, as shown. The hanger at point B connects to the clock by two wires that are tangent to the clock at points A and C.

A circle is shown with center at point E. There is a line segment connecting points B, D, E, and F. Segments DE and EF are radii of the circle. Segment DF is a diameter of the circle. Segment AB and BC are tangent to the circle at points A and C.

If the radius of the clock is 20 cm and the distance from the top of the clock at point D to the hanger at point B is 5 cm, what is the length from point A to point B?

5 cm
15 cm
20 cm
45 cm