In order to further improve the aforementioned operations, it is preferred that an opening area of the first intake air passage is reduced and {HEAD ~ an opening area} of {TAIL ~ the second intake air passage} is enlarged 
of
In order to further improve the aforementioned operations , it is preferred that an opening area of the first intake air passage is reduced and { HEAD ~ an opening area } of { TAIL ~ the second intake air passage } is enlarged
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH