  We compare contributions from the triangle diagram and the $D\bar D^*$ bubble
chain to the processes of $e^{+}e^{-}\rightarrow J/\psi\pi^{+}\pi^{-}$ and
$e^{+}e^{-}\rightarrow (D\bar D^*)^\mp\pi^{\pm}$. By fitting the $J/\psi\pi$
maximum spectrum and the $D\bar D^*$ spectrum, we find that the triangle
diagram cannot explain the new data from BESIII Collaboration at center of mass
at 4.23GeV and 4.26GeV, simultaneously. On the contrary, the molecular
assignment of $Z_c(3900)$ gives a much better description.
