Which of the following would justify step 6?
A) AAS
B) ASA
C) SAS
D) SSS

Answer: C) SAS
Explanation:
We have AD = DB which forms the first "S" in "SAS"
The second "S" is CD = CD
The angles between the two pairs of sides mentioned are the right 90 degree angles, which is what the "A" in "SAS" represents.