  Without excluding the contributions of factorizable Feynman diagrams in the
color space to the QCD sum rules by hand, we cannot obtain the conclusion that
the factorizable parts of the operator product expansion series cannot have any
relationship to the possible tetraquark bound states. The tetraquark couplings
$f_T$ are of the order $\mathcal{O}(N_c)$ rather than of the order
$\mathcal{O}(N^0_c)$ in the large $N_c$ limit, the conclusion "a possible
exotic tetraquark state may appear only in $N_c$-subleading contributions to
the QCD Green functions" is a paradox.
