The axiom of extensionality defines a set entirely by its members, without order or repetition. What consequence does this principle have for how we determine whether two separately described sets are identical?

C. They are identical if and only if each is a subset of the other

Equivalence in extensionality ignores description methods or counts; it requires mutual inclusion ($A \subseteq B$ and $B \subseteq A$). Confusing intensional definitions or cardinality with set identity overlooks that distinct predicates can pick out the exact same collection of objects.