Using charge conjugation and isospin invariance, show that
$$
\begin{aligned}
& D_u^{\pi^{+}}=D_u^{\pi^{-}}=D_d^{\pi^{-}}=D_d^{\pi^{\prime}}, \\
& D_u^{\pi^{-}}=D_u^{\pi^{+}}=D_d^{\pi^{+}}=D_d^{\pi^{-}}, \\
& D_s^{\pi^{+}}=D_s^{\pi^{-}} .
\end{aligned}
$$