  Transverse-mass spectra in Au+Au and Pb+Pb collisions in incident energy
range from 2A to 160A GeV are analyzed within the model of 3-fluid dynamics. It
is shown that dynamical description of freeze-out, accepted in this model,
naturally explains the incident energy behavior of inverse-slope parameters of
these spectra observed in experiment. Simultaneous reproduction of the
inverse-slopes of all considered particles (protons, pions and kaons) suggests
that these particles belong to the same hydrodynamic flow at the instant of
their freeze-out.
