Points A,B,C and D lie on a circle with centre O in this order. The central angles are ∠AOB=(x+20)∘,∠BOC=(2x−10)∘,∠COD=(x+40)∘ and ∠DOA=(2x+10)∘. Which statement about the lengths of the chords is correct?
(a) AB is the longest chord; BC and CD are equal and DA is the shortest chord.
(b) BC, CD, and DA are all equal in length and longer than AB.
(c) DA is the longest chord; BC and CD are equal and longer than AB.
(d) BC is the longest chord, followed by CD, then DA, then AB.