{HEAD ~ The unit} may also have {TAIL ~ a tubing} to allow oxygen or another treated gas to come in 
have
{ HEAD ~ The unit } may also have { TAIL ~ a tubing } to allow oxygen or another treated gas to come in
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH