ANSWER: If you answered (c), then you are not likely to confuse iron pyrites for the real thing, for a phantom is a bogus item. However, if you answered (a) you are still correct in a broader sense. The distinction between the two is that although all phantom stamps are by definition cinderellas not all cinderellas are phantoms.
According to the Cinderella Stamp Club in England, cinderellas include all back-of-the-book items such as bogus stamps, charity issues, advertising and exhibition labels, forgeries, and private local stamps. A fake is a stamp that is in some sense fraudulent, a regummed stamp being a good example. A forgery is an item that is intended to masquerade as an existing, valid postage stamp. As for the fowl fellows who produced the Audubon phantoms, they turned jailbirds and served time in Haitian prisons.