We are told that DO and BA are congruent and that OE and BC are congruent. We are also told that EO is congruent to OD. Since the distance that the chord is away from the center of the circle is directly proportional to the length of the chord, this means that BC and BA are congruent. Since the side of the corresponding arc is directly proportional to the length of the chord. This means that arcs BC and BA are congruent as well.