Lines are drawn inside the square of A to give B. Draw the same kind of lines in C.

B joins each corner of the square to the opposite corner: the 2 diagonals through the centre. A hexagon has 3 pairs of opposite corners, so it gets 3 lines through the centre, each from a corner to the opposite corner: (c). (a) has only 2 lines, (b) joins the middles of opposite sides instead of corners and (d) is a pentagon.