At a book fair, every stall that sells second-hand books also offers a discount on bulk purchases. Some of the stalls that offer a discount on bulk purchases do not accept card payment. Which of the following must be true?

The second-hand stalls all sit inside the group offering bulk discounts, but the stalls refusing cards are only 'some' of that larger group and may lie entirely outside the second-hand ones - or may include them. Both situations fit the facts, so the card question is left open. The first option treats a possibility as settled, and the third and fourth reverse or overstate the given relations.