  Applying the results of Ref.[1], we carry out the non-abelian bosonization
for a class of free fermion symmetry-protected topological states (SPTs). The
resulting boson theories are non-linear sigma models with topological $\theta$
term, thus unifying the field theory description of the (free) fermionic and
bosonic SPTs. Tuning $\theta$ from $0$ to $2\pi$ triggers the topological
trivial to non-trivial phase transitions. In addition, applying the same idea
to the symmetry-protected critical spin liquids, we obtain the NL$\s$ models
for spin SPTs living in one spatial dimension higher.
