{TAIL ~ A plurality} of {HEAD ~ connecting lines} are provided that couple a respective pairs of gas input and gas output lines 
{ TAIL ~ A plurality } of { HEAD ~ connecting lines } are provided that couple a respective pairs of gas input and gas output lines
TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH