Final answer:
The correct statement to complete the proof based on the properties of parallel lines in a triangle is that ∠BDE ≅ ∠BAC by the alternate interior angles theorem.
Step-by-step explanation:
The question deals with the properties of parallel lines and triangles. Specifically, it is related to the concept of similar triangles and the way parallel lines divide the sides of a triangle proportionally.
In ΔABC, segment DE is parallel to AC which invokes the theorem which states that if a line is parallel to one side of a triangle and intersects the other two sides, it divides those sides proportionally. The correct statement to complete the proof would be: ∠BDE ≅ ∠BAC; alternate interior angles theorem.
By the theorem, since DE is parallel to AC, the angles formed between these parallel lines and a transversal (line BD) are equal. Therefore, ∠BDE is congruent to ∠BAC since they are alternate interior angles formed by the parallel lines DE and AC, and the transversal BD.