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Answer:
D. ∠1 ≅ ∠3
Explanation:
In order to show the lines parallel, you must show how one of the angles 1 or 4 relates to one of the angles 2 or 3. Possibilities include ...
∠1 +∠2 = ∠3 +∠4 = 180°
∠1 = ∠3
∠2 = ∠4
The second of the possibilities listed here matches choice D.