The second intake air passage is closed when {HEAD ~ the first urging force} is smaller than {TAIL ~ the second urging force} 
is smaller than
The second intake air passage is closed when { HEAD ~ the first urging force } is smaller than { TAIL ~ the second urging force }
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL