What is a four-sided polygon called?
(a). triangle
(b). quadrilateral
(c). circle
(d). diagonal

Hint: Recall the definitions of a triangle, quadrilateral, circle, and diagonal. The word quadrilateral is of Latin origin and “Quadri” means four.

Complete step-by-step answer:
A polygon is defined as a flat or plane, a two-dimensional closed shape with straight sides. It does not have any curved sides. A polygon has three or more than three sides and if the sides are equal, it is called a regular polygon.

A three-sided polygon is called a triangle and it is the basic polygon.

A circle is a round two-dimensional figure that has no corners or edges. It can also be defined as a regular polygon with an infinite number of sides, so that its boundary is smooth.

A diagonal is a straight line connecting the opposite corners of a polygon through its vertex. The triangle does not have a diagonal.

A four-sided polygon is called a quadrilateral. It has four sides, four angles, and four vertices. A quadrilateral can also be regular or irregular. A regular quadrilateral is called a square.

The sum of the angles of a quadrilateral is 360°. The other special quadrilaterals are rectangle, parallelogram, rhombus, and kite.

Hence, the correct answer is option (b).

Note: This is a straightforward question and you might confuse yourself with the definition of a triangle and diagonal and choose any of them as the correct answer, which is wrong.