Answer:
The reasons for steps are
A. Given.
B. Definition of congruent angles.
C. Definition of bisector.
Explanation:
Given information: m∠ABC = m∠CBD.
To prove: BC bisects m∠ABD.
Proof:
(Given)
(Definition of congruent angles)
BC bisects m∠ABD (Definition of bisector)
Hence proved BC bisects m∠ABD.