选择D,意为:自从我离开这个城市,这个城市改变了不少.
因为出现since,表明用现在完成时,类似的有already（肯定）,yet（否定,疑问）,just,before,recently,still,lately,never,ever,never,twice,on several occasion,in the past few days/weeks/months/years,(up to)these few days/weeks/months/years,this morning/week/month/year,just,up to present,so far,up to now,till now,since+时间