which phrase best describes a figure with dimensions of 2 units by 2 units by 4 units and a volume of 16 cubic units

we know that

 A figure with dimensions of 2 units by 2 units by 4 units and a volume of 16 cubic units is a prism with a square base
length side of the square base=2 units
height of the prism=4 units
[volume of a prism]=2*2*4---->16 units³

or
is a prism with a rectangular base
length side of the rectangle base=4 units
width side of the rectangle base=2 units
height of the prism=2 units
[volume of a prism]=4*2*2---->16 units³

therefore
if the volume is 16 units ³ that means 
the solid figure can be filled with 16 cubes that each measure 1 cubic unit
so
the volume of one cube  is------> 1*1*1------> 1 unit³
volume of 16 cubes-----> 16*1 unit³------> 16 unit³

the answer is
the option A