  Recent observations on the GRB 000301c afterglow show that three breaks
appear in the R-band light curve, and in particular the decay slope at late
times is as steep as -3.0. This unusual afterglow is clearly inconsistent with
the standard afterglow shock model. Here we propose a non-standard model for
the unusual R-band afterglow of GRB 000301c. In this model, an
ultra-relativistic shock in a dense medium ("dirty environment")rapidly evolved
to the non-relativistic phase in initial 1 day. During such a phase, the shock
happened to be caught up with by two energetic shells ejected from the central
engine at two different times, and the shock was refreshed, leading to two
flattenings of the light curve. After each interaction between the shock and
shell, the afterglow decayed as $\propto t^{-3.0}$ if the electron distribution
index of the shocked medium, $p\approx 3.4$, derived from the optical spectrum.
Therefore, this model can provide an excellent explanation for the flattening
and steepening features of the GRB 000301c optical afterglow light curve. We
further point out that the energy injection shells ejected from the central
engine at later times may be material shells (e.g., in the massive star
progenitor models related to black holes) or radiation shells (e.g., in the
millisecond pulsar progenitor models).
