Change the narration: The teacher said, "Two and two is four".

The teacher said that two and two will be four.

The teacher said that two and two was four.

The teacher said that two and two is four.

None of these

The teacher said that two and two is four.

Universal truths or facts remain unchanged in indirect speech.

Since "Two and two is four" is a mathematical fact, the verb "is" stays the same.