  As a test of the color-singlet mechanism of the nonrelativistic QCD (NRQCD)
factorization approach, we consider the exclusive two-quarkonium productions in
electron-positron annihilation e+ e- -> eta_c + gamma and e+ e- -> J/psi +
J/psi at B factories. The cross sections are computed to the next-to-leading
order in alpha_s and are resummed to all orders in half the relative velocity v
of the charm quark in each meson rest frame. The available theoretical
prediction of the cross section for e+ e- -> J/psi + eta_c at the same level of
theoretical accuracies is consistent with the available experimental data.
Those for e+ e- -> eta_c + gamma and e+ e- -> J/psi + J/psi that are computed
new in this work can be tested against the data from future super B factories.
