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