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