Answer :- A. Corresponding parts of two congruent triangles are congruent.
Complete proof :-
Statement reasons
1. ABCD is a kite 1. given
2. AB ≅ BC, BP ⊥ AC 2. definition of kite
3. BP ≅ BP 3. reflexive property
4. △ABP ≅ △CBP 4. HL theorem
5. AP ≅ CP are congruent 5. Corresponding parts of two congruent
triangles
6. BD bisects AC at point P 6. definition of bisect
- <em>If two triangles are congruent then their corresponding parts are congruent.</em>
So, option A must be the reason for step 5 which completes the proof.