Question

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Explanation:

Step1: Identify consecutive interior angles

Since $\overleftrightarrow{AB} \parallel \overleftrightarrow{CD}$, $\angle ABD$ and $\angle BDC$ are consecutive interior angles, so they are supplementary:
$\angle ABD + \angle BDC = 180^\circ$

Step2: Substitute congruent angles

We are given $\angle ABD \cong \angle DCA$, so by substitution, we get:
$\angle DCA + \angle BDC = 180^\circ$

Answer:

Statements	Reasons

(This fills the missing row in the two-column proof)