IN: Which person is he?
Caesar the ape found out the door code by watching Morris, because he was careless when typing in the code.
OUT: Morris

IN: Which person is they?
MIT accepted the students, because they had good grades.
OUT: the students

IN: Which person is she?
Jill loves Jamie and she does not feel the same way.
OUT: Jamie

IN: Which person is it?
The painting was at the museum because it was on display.
OUT:
The painting