Question

A. triangle sum theorem b. definition of supplementary c. linear pair postulate

Answer 1

For

4. We see that angles A, D and ABD are angles in a triangle.

So also angles C, E, and CBE.

Therefore, the reason here is the sum of angles in a triangle.

5. Now, angle ABD, angle DBE, and angle CBE all sum up to 180 degrees, and they all lie on a straight line.

Therefore, the reason here is; angles on a straight line.