1. Vertical angles are congruent: a) we're proving that two angles are congruent (we use ≅), and it just happens that those two angles are vertical (opposite angles on two intersecting lines).
2. SAS congruence: It is one of the last three, since we're trying to prove the triangles' congruence, and it is SAS, because our given gives us two pairs of congruent lines, and we find that the angle between them are congruent.