  We show that the clumpy structure of star-forming regions can naturally
explain the fact that 50-70% of GRB afterglows are optical``dark.'' We also
show that dust echos from the GRB and its afterglow, produced by the clumpy
structure of the star-forming region in which the GRB occurs, can lead to
temporal variability and peaks in the NIR, optical, and UV lightcurves of GRB
afterglows.
