The mass flow controllers 94 and 96 control {TAIL ~ the flow rates} of {HEAD ~ the boron} trichloride 
The mass flow controllers 94 and 96 control { TAIL ~ the flow rates } of { HEAD ~ the boron } trichloride
OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH