What happens if you don’t bother to register a copyright and someone pirates your work five years after it is published?

a) the copyright is lost by then; b) it makes no difference whether you register—ever; c) it makes no difference unless you also fail to include the copyright notice; d) the copyright is still valid, but your remedies in an infringement lawsuit will be more limited; e) the copyright will expire much sooner, but you can still sue the infringer.

D