Question 23 • Math 3
If triangles ABC and CDA are congruent, their corresponding sides have equal lengths. In that correspondence, side BC matches side AD, so AD = BC. Choice D gives a valid sequence; the other choices either use similarity, which does not establish equal side lengths, or rely on opposite sides of a parallelogram without first establishing that ABCD is a parallelogram.
AI-written and checked against the verified answer.