Epithelium cells are type of cells that has a simple cuboidal epithelium that consists of only a single layer of cells that are cube-like or cuboidal in shape. In the question given cell is similar to these cells.
These cells have large, spherical nuclei present in the center. These cells are cube-shaped cells which support the option D to be correct.
The diagram shown in the given question ids more like a cube. A cube is a three dimensional structure having six faces(square shaped) and 12 edges and eight vertices. Volume of cube can be determined by taking cube of it's one edge. Surface area of cube is six times to the square of its edge.
