Final answer:
Statement A must be true: m∠ABD = m∠ABC
Step-by-step explanation:
Given that Ray B A bisects ∠DBC, we can determine the following:
- m∠ABD = m∠ABC (By definition of angle bisector)
- A line bisects an angle when it divides that angle into two congruent angles.
Therefore, statement A is true: m∠ABD = m∠ABC