Are the following statements true or false?

(a) If there is an atom present at the corner of a unit cell, there must be the same type of atom at all the corners of the unit cell.

(b) A unit cell must be defined so that there are atoms at the corners.

(c) If one face of a unit cell has an atom in its center, then the face opposite that face must also have an atom at its center.

(d) If one face of a unit cell has an atom in its center, all the faces of the unit cell must also have atoms at their centers.