Question

A simple closed curve made up of only line segment is called
[a] curve
[b] polygon
[c] surface
[d] concave

Answer 1

Hint: Think which of the closed figures is made of line segments only. Recall the definitions of a curve, a polygon, a surface and a concave figure.

Complete step-by-step answer:
A curve in Euclidean geometry is any geometrical figure which starts as a line but deviates from being straight eventually. Below is an example of a curve.

A continuous boundary dividing a three-dimensional space into two reasons is called a surface. The surface of a sphere in 3D is an example of a surface. An XY-plane in XYZ-space is an example of a surface.
A concave closed figure is a figure in which there exist two points A and B inside the figure, such that the line segment AB does not completely lie inside the surface,

ABCDE is an example of a concave figure because there exist points F and G inside ABCDE such that FG does not completely lie inside ABCDE.
A polygon is a closed figure made up of line segments only. A polygon has three or more than three sides and can be concave or convex.
Hence option [b] is correct.

Note: Although it may seem that concave figures are also made up of line segments only, it is not correct. Consider the following curve.

ABCD is concave. But ABCD is not made up of line segments only.