  An optimal-observable analysis of the angular and energy distributions of the
leptons and bottom quarks in the process e+e- --> tt-bar --> l^{+-}/b(b-bar)...
has been performed in order to measure the most general top-quark couplings to
gauge bosons at polarized linear colliders. The optimal beam polarization for
determination of each coupling has been found. A very sensitive test of CP
violation in tt-bar production and decay has been proposed.
