IN: Which person is it?
The elephant trampled a fish and it died.
OUT: a fish

IN: Which person is they?
NATO forces did precision predator strikes for the Libyan rebels because they did not have the capabilities themselves.
OUT: Libyan rebels

IN: Which person is they?
Chase Freedom provides quarterly bonuses as incentives for accounts, since they want them to use their card.
OUT: Chase Freedom

IN: Which person is him?
Bill was robbed by John, so the officer arrested him.
OUT:
John