Answer:- "ASA congruence postulate" is the reason which completes the proof.
Explanation:-
Given:- AD | | BC and AD = BC
To prove:- ΔADM ≅ΔBCM
Proof:- Statement Reason
1. AD=BC [Given]
2. ∠1=∠3 ; ∠2=∠4 [If lines parallel, then alternate interior angles are equal]
3. ΔADM ≅ΔBCM [ASA congruence postulate]
Thus, "ASA congruence postulate" is the reason which completes the proof.