When {HEAD ~ an abnormal operation} occurs in {TAIL ~ the production line}, it is thus easy to find which working group is in trouble 
occurs in
When { HEAD ~ an abnormal operation } occurs in { TAIL ~ the production line } , it is thus easy to find which working group is in trouble
OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH