Identify the diagram that best represents the relationship among the given classes.
Metal, Oxygen, Copper

Let's establish the relationship among the three given terms:
Copper is a specific chemical element that belongs entirely to the category of Metals. Therefore, the circle representing Copper must be completely enclosed inside the circle representing Metals.

Oxygen is a non-metal gas and is completely distinct from both Metals and Copper. Therefore, the circle representing Oxygen must be drawn entirely separate from the other two.

This structural relationship is perfectly represented by a large circle (Metals) containing a smaller circle (Copper), alongside an entirely separate, disjoint circle (Oxygen). This matches Option A.