Answer
The correct conclusion is $\overset\longleftrightarrow{BC}\parallel\overset\longleftrightarrow{AD}$
Work Step by Step
$\overset\longleftrightarrow{DC}$ is the transversal with the marked angles, so the Converse Same-side Interior Angles Theorem tells us the two lines intersected by $\overset\longleftrightarrow{DC}$ are paallel.
