Assuming the atomic radius is r, the volume of unit cell for the crystal structures of simple cubic, body centred cubic, and face centred cubic can be calculated by ( ).

A、Forthecrystalstructuresofsimplecubic:volumeofunitcell=3r·3r·3r=27r^3
B、Forthecrystalstructuresofsimplecubic:volumeofunitcell=2r·2r·2r=8r^3
C、Forthecrystalstructuresofbodycentredcubic:volumeofunitcell=(4r3^0.5)^3
D、Forthecrystalstructuresoffacecentredcubic:volumeofunitcell=(4r2^0.5)^3