Missing keywords in url, help me !

Hi all master !
I'm using vbseo 3.60 , but url errors missing keywords.
I want my url is full :
http://domain.com/can-ban-du-an-bat-dong-san-tai-ha-noi-28.html
but my url missing "an" :
http://domain.com/can-ban-du-bat-dong-san-tai-ha-noi-28.html

Please view images :



I hope yours help me, thanks u very much !

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