6vi. When a surface is such that the right line joining any two arbitrary points in it lies wholly in the surface, it is called a plane. A plane is perfectly flat and even, like the surface of still water, or of a smooth floor.

What is the purpose of the analogy in paragraph 6?

A) to exaggerate the likeness between two things
B) to offer a more technical definition of a concept
C) to explain a less familiar concept using a known one
D) to provide a contrast between one object and another