Which of the following statements are correct?

• A

  A NaCl type AB crystal lattice can be interpreted to be made up of two individual f.c.c unit cells of A and B fused together in such a manner that the corner of one unit cell becomes the edge centre of the other

• B

  In a face-centred cubic unit cell, the body centre is an octahedral void

• C

  In f.c.c. unit cell, octahedral and tetrahedral voids are equal

• D

  Tetrahedral voids = 2 × octahedral voids, is true for only c.c.p and h. c. p.