  From a theoretical point of view, we propose an experimental method to
determine the pairing symmetry of iron pnictides. We focus on two kinds of
pairing symmetries, $s_{+-}$ and $s_{++}$, which are strong candidates for the
pairing symmetry of iron pnictides. For each of these two symmetries, we
calculate both the density and spin response functions by using the two-band
BCS model within the one-loop approximation. As a result, a clear difference is
found between the $s_{+-}$- and $s_{++}$-wave states in the temperature
dependence of the response functions at nesting vector $\bf{Q}$, which connects
the hole and electron Fermi surfaces. We point out that this difference comes
from the coherence effect in the two-band superconductor. We suggest that the
pairing symmetry could be clarified by observing the temperature dependence of
both the density and spin structure factors at the nesting vector $\bf{Q}$ in
neutron scattering measurements.
