IN: Which person is they?
The students read the books because they were interesting.
OUT: the books

IN: Which person is he?
Joe earned more money than Rob on the Price is Right because he kept guessing wrong.
OUT: Rob

IN: Which person is he?
Jean is making fun of Kyle because he won.
OUT: Jean

IN: Which person is they?
Knights preferred dragons over horses because they could not fly.
OUT:
horses