Amy constructed this figure by using a compass to draw circle C and then a straightedge to draw diameter AB through point C. Then, with the compass still set equal to the radius of the circle, Amy drew two arcs centered at point B and labeled the points of intersection D and E. She used the straightedge to draw chords AD, AE, and DE. Amy notes that arcs ADB and AEB are semicircles and that ΔBDC is equilateral. Because ∠BCD is a central angle, she can say that = 60°. She uses these facts to determine = = = 120°. Finally, she concludes ΔADE is equilateral because congruent arcs are intercepted by congruent chords. Why is ΔBDC is equilateral? A. Triangle BDC is equilateral because diameter AB is a perpendicular bisector of chord BD. B. Triangle BDC is equilateral because arcs BD and BE are two arcs with the same radius and center. C. Triangle BDC is equilateral because the sum of the three angle measures in ΔADE is the same as the measure of a semicircle. D. Triangle BDC is equilateral because the distance between all three vertices is equal to the radius of the circle.