Volume of a cylinder = πr²h. Substitute r=12 and h=70: volume = 3.14 × 12 × 12 × 70 = 31651.2 cubic mm. Think of a cylinder as many equal circular layers stacked up. So we find the circular base area πr² and multiply by the height. The answer is in cubic units, so the correct choice is 31651.2 mm³.