Which option describes a layer?

• A. A thin sheet of a certain substance
• B. Different tiers that make something up
• C. A substance that is above or under another substance
• D. The outermost coating

Answer: (A)

A layer is a single sheet of material that sits between other parts of a structure. This option describes a thin sheet of a substance, which matches the common idea of a layer as a flat, plate-like piece forming part of something larger.

The other ideas lean more toward concepts rather than the thing itself. Describing “different tiers” points to multiple levels, not a single sheet. Saying a substance is above or below another speaks to a relationship, not the object that constitutes a layer. The outermost coating refers to a surface covering, which is a type of layer but is more specific; the general notion of a layer is best captured by a single thin sheet.