Constructions & proofs

In quadrilateral ABCD, let P be the intersection of diagonals AC and BD. Given that ∠DAC = ∠DBC, the following proof shows that the four points A, B, C, and D lie on the same circle, and uses this fact to prove that ∠ABD = ∠ACD.

[Proof]

Points A and B lie on the same side of line CD, and by assumption, ∠DAC = ∠DBC.

Since points A and B lie on the same side of line CD and ∠DAC = ∠DBC, by [ A ], the four points A, B, C, and D lie on the same circle.

Therefore, the [ B ] subtended by arc AD are equal, so

∠ABD = ∠ACD.

Which of the following is the most appropriate combination of terms to fill in blanks [ A ] and [ B ]?