The figure that is a line is the third figure at the Bottom Right which is C. Figure C.
Which figure is a line
A line has no width or thickness. It is often represented as a simple, infinitely thin path.
A line is perfectly straight, meaning that any two points on the line can be connected by a straight path without any curvature.
A line extends infinitely in both directions. There is no endpoint, which means it goes on forever.
This is why the figure in Figure C is a line because it extends indefinitely.