在定语从句中,一般情况下,介词+关系代词=关系副词,介词提前是把介词放在关系代词的前面就可以.
此题中把to放在whom之前就行,另外在这个等式变换中,这个关系代词并不包括that,所以介词提前时,whom或其他关系代词都不能换成that.
相关例句：
She is the gilr that/whom I am looking for.
She is the girl for whom I am looking.
This is the room that/which I live in.
This is the room in which I live.