IN: Which person is it?
The elephant trampled a fish and it continued on its way.
OUT: The elephant

IN: Which person is him?
Jacob misled Amen so David fired him.
OUT: Jacob

IN: Which person is they?
American Airlines offers upgrades for their preferred passengers since they want them to continue flying with them.
OUT: American Airlines

IN: Which person is they?
Professors give a lot of advice to students, but they rarely care.
OUT:
students