IN: Which person is they?
The invaders showed no mercy to the defenders, but they would not surrender anyway.
OUT: the defenders

IN: Which person is he?
The master rewarded the dog because he was a good companion.
OUT: the dog

IN: Which person is they?
The US Health inspection board shut down several food factories, but they discovered that many rules and regulations were violated.
OUT: The US Health inspection board

IN: Which person is they?
The squirrels buried the nuts so they would not lose them.
OUT:
The squirrels