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,onseveraloccasion,inthepastfewdays/weeks/months/years,(upto)thesefewdays/weeks/months/years,thismorning/week/month/year,just,uptopresent,sofar,uptonow,tillnow,since+时间