Cis the center of the circle. in order to prove that opposite angles of a quadrilateral inscribed in a circle are supplementary (in this case m∠edg + m∠efg = 180°), which fact is most important to know? a) m∠efd = m∠gfd b) m∠ecf = m∠dcg c) m∠edg = m∠efg d) m∠edg = 1 2 m∠ecg