These units may also have other pieces such as microphones and {HEAD ~ speakers} in {TAIL ~ order} to allow communication to be facilitated in difficult circumstances 
in
These units may also have other pieces such as microphones and { HEAD ~ speakers } in { TAIL ~ order } to allow communication to be facilitated in difficult circumstances
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH