branliest on this volume on a cube volume question

Which cube is a unit cube?

1. a cube that is 2 feet long, 2 feet tall, and 2 feet high

2. a cube that is 5 meters long, 5 meters wide, and 5 meters high

3. a cube that is 3 yards long, 3 yards wide, and 3 yards high

4. a cube that is 1 inch long, 1 inch wide, and 1 inch high