  We reveal that the temperature dependence of the basal-plane normal-state
electrical resistance of optimally doped YBa$_2$Cu$_3$O$_{7-\delta}$ single
crystals can be with great accuracy approximated within the framework of the
model of s-d electron-phonon scattering. This requires taking into account the
fluctuation conductivity whose contribution exponentially increases with
decreasing temperature and decreases with an increase of oxygen deficiency.
Room-temperature annealing improves the sample and, thus, increases the
superconducting transition temperature. The temperature of the 2D-3D crossover
decreases during annealing.
