Your answer is A. another writer's interpretation of a subject.
Since another writer is the one who wrote the information, you have to cite the source to properly acknowledge that the information was not created by you.
You do not have to cite common knowledge because it is something that most people already know.
You do not have to cite your own interpretation or opinion of the subject because it is your own work.
For example in New Zealand you can't vote if you're under 18 or in prison In the UK you can't vote if your certified mad I'm not so sure about the US but it may have some of these rules. Hope it helps a bit!
