Answer:
b. Parallelogram.
Step-by-step explanation:
A parallelogram is a four-sided mathematical figure with two sides parallel to each other. This simple quadrilateral also has two opposite sides of equal length and the interior opposite angles are of equal measures. 
A parallelogram is also a type of polygon with four sides, much like a square, a rhombus, or a rectangle. All these geometrical figures are used in mathematical systems. 
Thus, the correct answer is option b.