Final answer:
The correct option that proves ∠ABD ≅ ∠ACD is (a) ASA (Angle-Side-Angle) Congruence.
Step-by-step explanation:
By the given information, we know that triangle △ABC is isosceles with AB ≅ AC. Since AD bisects ∠BAC, we can split this isosceles triangle into two congruent triangles, △ABD and △ACD.
The reason for this is that the angles opposite the congruent sides are also congruent.
Therefore, the correct option that proves ∠ABD ≅ ∠ACD is (a) ASA (Angle-Side-Angle) Congruence.