Answer:
A. Angle Addition Postulate
Explanation:
<AMC, <CMD, and <DMB are three angles on a straight line which makes up <AMB.
According to angle addition postulate, the measure of <AMB is the sum of these three angles.
Therefore, angle addition postulate justifies Allison's statement that states:
<AMC + <CMD + <DMB = <AMB.
Definition of supplementary angles deals with two angles adding up to equal 180°. So, definition of supplementary angles definitely does not justify his statement.
Segment addition nor construction of an angle bisector do not also justify his statement.
The right answer is: A. Angle Addition Postulate.