词汇网络: upon

In a higher place than something or someone.

Physically in contact with and supported by a surface.

Moving to a position on the surface of.

Atop is a preposition that means on the top of or resting on the summit of something. It is used to describe the physical position of an object or person sitting or placed directly upon a surface or structure.

Not any of a group of people or things. It represents zero or a total lack of something that was mentioned or is being discussed.