17. Which of the following is not a polygon? A. quadrilateral B. pentagon C. semi-circle 18.How many sides does a triangle have? A. three B. four C. five D. six 19. What is the sum of the interior angle in a triangle? A. 90° B. 180° C. 220° D. 360° 20. What is a polygon? A closed figure made up of crossed line segments B. A closed figure made up of straight line segments C. An open figure made up of crossed line segments D. An open figure made up of straight line segments
