Answer:
Third option: Definition of Congruent angles.
Step-by-step explanation:
For this exercise it is important to know the definition Congruent angles.
Congruent angles are defined as those angles that have equal measure.
The symbol used for Congruent angles is the following:
≅
Keep the explanation above on mind.
In this case, you know that [tex]\angle ABC[/tex] measures 90 degrees (This is also known as "Rigth angle"):
[tex]\angle ABC=90\°[/tex]
And you can observe in the table attached that the measure of [tex]\angle ABD[/tex] is also 90 degrres:
[tex]\angle ABD=90\°[/tex]
Therefore, since they have exactly the same measure, these angles are congruent. Then:
[tex]\angle ABC[/tex] ≅ [tex]\angle ABD[/tex]
Based on this, you can identify that the missing reason number 8 is: Definition of Congruent angles.
