13. Which of the following statements is (are) false?
I. The layering in a hexagonal closest-packed structure is aba.
II. A body-centered cubic unit cell has four atoms per unit cell.
III. For unit cells having the same edge length, a simple cubic structure would have a smaller density than a body-centered cube.
IV. Atoms in a solid consisting of only one element would have six nearest neighbors if the crystal structure were a simple cubic array.

(A) I
(B) II
(C) II, III
(D) I, IV
(E) II, III, IV