Answer:
a. Right triangle (scalene)
b. Parallelogram
c. Square
d. Concave Quadrilateral
Explanation:
a. Three sides makes it a triangle, there is a right angle (box on the angle means it is 90 degrees) and all side lengths are different (scalene)
b. Parallelogram means that there are four sides, and opposite sides are parallel, meaning if they were to continue, they would never touch.
c. Squares have four equal sides with all angles being right angles
d. Four sides makes it a quadrilateral, and one of the interior angles are greater than 180 degrees, making it concave.
I hope this helps, if you need anything explained let me know.