How are the guards set up on both sides of DMZ? What does that tell you of either side?

In the diagram below dab and dac are adjacent angles

The great scientist alfred wegener proposed that continents have moved, while other scientists such as t.c.chamberlin argued against wegener. wegener's ideas eventually won, and are now widely accepted, because: a) wegener's ideas were more beautiful, and so were favored by the intellectual elite.b) wegener's ideas did a better job of predicting the results of new observations and experiments.c) wegener's ideas appealed to dead white european males, whereas chamberlin's didn't.d) wegener's ideas appalled dead white european males, and we all know that in this politically correct era,dead white european males cannot get a fair shake.e) wegener won the nobel prize.

The blue segment below is a diameter of oo. what is the length of the radius of the circle?