Which statement describes a unit cube?
a cube that is 1 foot long, 1 foot wide, and 1 foot high
a cube that is 5 centimeters long, 5 centimeters wide, and 5 centimeters high
a cube that is 1 centimeter long, 1 foot wide, and 1 yard high
a cube that is 4 inches long, 4 inches wide, and 4 inches high