  The dynamic response functions of strongly interacting fermion gas in
homogeneous space are investigated in a virial expansion to second order. The
density response function exhibits transition from atomic to molecular
response, as the interaction strength increases and the system undergoes
BCS-BEC crossover. The qualitative features of density and spin response agree
with measurements from the Bragg spectroscopy experiments. The virial response
is exact at low density and high temperature, therefore providing a benchmark
for many-body response.
