C is the incenter of isosceles triangle ABD with vertex angle ∠ABD. Does the following proof correctly justify that triangles ABC and DBC are congruent?
a. There is an error in line 1; segment BC should be an angle bisector.
b. The proof is correct.
c. There is an error in line 3; segments AB and BC are congruent.
d. There is an error in line 5; the ASA postulate should be used.