a. m<CBA = m<DBA because of the definition of an angle bisector (angle bisector cuts the angle in half) We are also told that segment BD and Segment BC are congruent.
We don't know if segment AC and AD are congruent so we can't say those angles (the other two) are congruent.
b. point A and B will stay fixed because they are colinear to segment AB (on the same line)
c. Those two are needed because If those are true we can prove that they are congruent by SAS (Side Angle Side)
d. the reflection an prove that the lines and angles are congruent.
