Red-clay bricks have a density of approximately 2000 kg/m^3. Air has a density of 1 kg/m^3. Which of the following has the lowest mass? Choices:
(I) 2 m^3 of bricks.
(II) 4 m^3 of bricks.
(III) 6000 m^3 of air.
(IV) 10,000 m^3 of air.
Your answer: