$d$ and $m$ are the parallel tangent at $A$ and $B$. The tangent at $C$ makes an intercept $DE$ between $d$ and $m$. Hence $\angle{DFE}$ = ________

Question

$\begin{array}{1 1}(a)\; 45^{\circ} \\(b)\; 60^{\circ} \\(c)\;90^{\circ} \\(d)\; 30^{\circ} \end{array}$