Points A,B,C and D are in a plane such that AB subtends an angle of 38∘ at C and also 38∘ at D, with C and D on the same side of AB. Which of the following conclusions is correct?
(a) AB is a diameter of the circle through A and B
(b) AC=AD
(c) A,B,C and D are concyclic
(d) △ABC≅△ABD