Preferably, {HEAD ~ the moisture} may be added to achieve {TAIL ~ a predetermined level} of humidity in the selected gas component 
added to achieve
Preferably , { HEAD ~ the moisture } may be added to achieve { TAIL ~ a predetermined level } of humidity in the selected gas component
OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH