Which statement describes a unit cube?

a cube that is 1 inch long, 1 foot wide, and 1 yard high
a cube that is 2 feet long, 2 feet wide, and 2 feet high
a cube that is 1 meter long, 1 meter wide, and 1 meter high
a cube that is 1 foot long, 2 feet wide, and 3 feet high