i have many friends,some ()are businessmen

i have many friends,some ()are businessmen
of them还是Ofwhom

答：of whom
解析：观察此题,无并列连词,所以需用介词+关系代词引导非限制性定语从句.根据句子意思“我有许多朋友,其中一些是商人.”得知：“朋友当中的一些some of friends”中含介词“of”,用whom代替friends后为of whom.