Answer:
AAS Congruence Theorem
Explanation:
According to the problem,

So, we know by defintion that all three internal angles must sum 180°,

Both sums are equal

As you can observe, we have all three correspoing angles equals, we could demonstrate the triangles congruence by AAA postulate, but it's not a choice.
The easiest form to demonstrate this congruence is using AAS congruence theorem, which state if two pair of corresponding angles are congruent, and one pair of corresponding sides is congruent, then those triangles are congruent. And we have since the beginning two angles and one side all congruents.
Therefore, we can demonstrate it with AAS Congruence Theorem.