IN: Which person is it?
Excalibur spent time with the stone because it needed a place to wait.
OUT: Excalibur

IN: Which person is he?
Mike cut his finger while watching Chef Michaels on TV because he was not paying attention to his task at hand.
OUT: Mike

IN: Which person is they?
U.S. Authors are fighting against Amazon's book lending program because they allow users a free book every month.
OUT: Amazon's book lending program

IN: Which person is they?
The US army fought the Taliban because they are the root of much terrorism.
OUT:
the Taliban