what exam is to be given to take admission in harvard or oxford?what preparation is required?please tell some detail of this exam??/

hi nitika,welcome to https://shiksha.com and for getting admission in us universities we have some exams like gre and toefl so if we qualify and if we get good marks in these exams u have a chance to get a seat in oxford or Harvard universities so u better prepare for that exams if u have above 90%i