Count the sides of every shape in a row. Which shape should fill the empty cell so that the bottom row matches the others?

In the top row $3+4+5=12$ sides and in the middle row $6+3+3=12$ sides. The bottom row already has $4+4=8$, so it needs a shape with $12-8=4$ sides: a square, (c). (a) gives 13 sides, (b) 14 and (d) 11.