{HEAD ~ A method} 1, wherein {TAIL ~ the metal} made Raschig rings are made of stainless steel 
wherein
{ HEAD ~ A method } 1 , wherein { TAIL ~ the metal } made Raschig rings are made of stainless steel
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH