system
A chat on subreddit /r/NoStupidQuestions
human
Yeah, but is it who or whom?
gpt
Whom. Follow the m's–if you can replace it with them/him then it's whom. If you replace it with they/he/she then it's who.

So to use your sentence as an example (after some rearranging for clarity) "...they have selected him" -&gt; "...they have selected whom" -&gt; "...whom they have selected"