英语关系代词英语的关系代词which whom as 在用于非限定从句时所指代的可以是一个词也可为一个句子.但为一个词时

英语关系代词英语的关系代词which whom as 在用于非限定从句时所指代的可以是一个词也可为一个句子.但为一个词时,在位置上除了代替紧跟其前面的先行词外,替代的词也可在句中的任意位置么?如 Present at the meeting were almost experts on DNA,most of whom come from the USAwhom替代的词是最前面的主语.