IN:
Multi-choice problem: [he]

The teacher told the student that he needed to practice.

OUT:
the student

IN:
Multi-choice problem: [they]

The teachers failed the students because they answered the test incorrectly.

OUT:
the students

IN:
Multi-choice problem: [he]

Bob cooked omelets for Jack, because he knew how.

OUT:
Bob

IN:
Multi-choice problem: [they]

The Union defeated the Confederates in the Civil war since they had better resources and numbers.

OUT:
The Union