A parallelogram is defined as a quadrilateral with BOTH pairs of opposite sides parallel.<br><br>
&bull; AB \( \parallel \) DC AND AD \( \parallel \) BC must both be true.<br>
&bull; Options A and B each only state one pair of parallel sides &mdash; insufficient.<br>
&bull; Option D is not necessarily true: adjacent angles are only equal in a rectangle.<br><br>
Final Answer: AB is parallel to DC and AD is parallel to BC