Punishing someone for an action that did not used to be a crime is an example a. an ex post facto law b. habeas corpus c. a “necessary and proper” law d. a bill of attainder.

The correct answer that would complete the given statement above would be option A. Punishing someone for an action that did not used to be a crime is an example of an ex post facto law. The Ex post facto law, a Latin which means "After the fact" Law, is a law that makes illegal an act that was legal when committed.