This structure is particularly useful if {HEAD ~ the supply} 94 includes {TAIL ~ a quantity} of toxic gases 
includes
This structure is particularly useful if { HEAD ~ the supply } 94 includes { TAIL ~ a quantity } of toxic gases
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH