Which of the following statements about regular languages is NOT true?

Correct answer: Every subset of a regular language is regular

Explanation:

• Every language has a regular superset: True. For any alphabet Σ, Σ* is regular and contains any language over Σ.

• Every language has a regular subset: True. The empty set is a subset of every language and is regular.

• Every subset of a regular language is regular: False. A regular language can contain non-regular subsets. For example, over the alphabet {a,b}, the regular language {a,b}* contains the subset {a^n b^n : n ≥ 0}, which is not regular (e.g., by the pumping lemma).

• Every subset of a finite language is regular: True. Any subset of a finite language is finite, and all finite languages are regular.