The proposition "Jack is X" and the proposition "Jack is Y" are equivalent if:

A) X means the opposite of Y
B) X is a concept that includes Y
C) Y is a referent of the concept X
D) X and Y are both referents of the same concept
E) X means the same as Y

Equivalent

Equal in value, function, or meaning, often referring to items that can be substituted for one another in specific contexts.

Concept

An abstract idea or a mental symbol that typically represents a class of things or phenomena.

Referent

The real object or item in existence that is signified or represented by a word or expression.