Ans: D
Since $AE//BD$, then
Since $AE//BD$, then
$\begin{array}{rcl}
\angle FAE & = & 70^\circ \\
\angle FAD + 20^\circ & = & 70^\circ \\
\angle FAD & = & 50^\circ
\end{array}$
Since $A$, $B$, $C$ and $D$ are four points on the circle, then we have
$\begin{array}{rcl}
\angle CBD & = & \angle FAD \\
& = & 50^\circ
\end{array}$
