the doctor whon或who you are looking for is in the room 这个句子中为什么用whom或who都可

因为这个词在剧中做look for的宾语

现代英语中,当引导词在定语从句中充当宾语时,who或者whom都可以充当定语从句的引导词,前提是,引导词前没有介词.
如：
He is the person who/whom/that/不填 I talked to yesterday.
但这种情况只能用whom
He is the person to whom I talked yesterday.