英文句型排列請教 - 社會議題

從教科書上看來的Theproblemofairpollutionincitieshasbecomemoreandmoreserious.為什麼cities後面接的是has?另外可以寫成以下方式嗎?Incities,theproblemofairpollutionhasbecomemoreandmoreserious.Theproblemofairpollutionhasbecomemoreandmoreseriousincities.請問還有其他寫法嗎?以目前這個句子中現有的單字下去排列...Showmore