AHSME 1968 Problem 6

Let side $AD$ of convex quadrilateral $ABCD$ be extended through $D$, and let side $BC$ be extended through $C$, to meet in point $E.$ Let $S$ be the degree-sum of angles $CDE$ and $DCE$, and let $S'$ represent the degree-sum of angles $BAD$ and $ABC.$ If $r=S/S'$, then: $\text{(A) } r=1 \text{ sometimes, } r>1 \text{ sometimes} \\ \text{(B) } r=1 \text{ sometimes, } r1 \text{(E) } r=1$