Answer: option A. the surface of a flat plane.
Justification:
A plane in geometry is an infinite surface that does not have curvature, which means it is flat
It is an idealization and it does not have thickness and is unlimited in width and length. Those are the properties of a plane.
Here you have some examples that may represent the idea of a plane:
1) The surface of a hardcover book
2) The surface of the floor of a house
3) The surface of a wall
4) The surface of a flat mirror.
So, the clue to distinguish the correct answer is the word flat.
Rgarding the other options, the B. the edge of a desk describes a line, the C. describes a curve, and the D. describes a point.