Ans: C
Join $OB$ and $OC$. Let $\angle COD = x$.
Join $OB$ and $OC$. Let $\angle COD = x$.
$\because \overparen{AB} = \overparen{BC} = 2\overparen{CD}$,
$\therefore \angle AOB = \angle BOC = 2\angle COD = 2x$.
Hence, we have
$\begin{array}{rcl}
70^\circ + 2x + 2x + x & = & 360^\circ \\
x & = & 58^\circ
\end{array}$
Therefore, we have
$\begin{array}{rcl}
\mbox{reflex } \angle BOD & = & 2(58^\circ)+70^\circ \\
& = & 186^\circ
\end{array}$
Hence, we have
$\begin{array}{rcl}
\angle BCD & = & \dfrac{1}{2} \times \mbox{reflex }\angle BOD \\
& = & \dfrac{1}{2} \times 186^\circ \\
& = & 93^\circ
\end{array}$
