Bonjour!
For A, the two angles are congruent by the Corresponding Angles are Congruent Theorem/Postulate.
For B, the two angles are congruent by the Vertical Angels are Congruent Theorem/Postulate.
As for C, the two angles are congruent by the Same Side Exterior Theorem/Postulate.(Though I am uncertain if that is the correct name for this one)
Hope that helps :)
