  The observed late-type WC Wolf-Rayet stars (WC7-9) with low luminosity below
$\rm \log L/L_{\odot} < 5.4$ in the HR diagram cannot be reproduced
satisfactorily by the evolutionary track of single stars. The mass transfer due
to Roche lobe overflow drastically modifies the internal structure and surface
compositions of two components. Therefore, binaries provide a very promising
evolutionary channel to produce these WC stars.
