Given the task definition and input, reply with output. You are given a background paragraph that describes one or more causal or qualitative relationships such as a relationship in economics or a scientific law and a story that makes use of the concepts or the relationship described in the provided paragraph. You need to come up with a question about the story that requires an understanding of the relationship described in the background paragraph. The generated question should not be answerable without both the background and story. Write a question about the story that requires a relationship in the background paragraph to answer. Check whether your question requires both the background paragraph and the story to answer. If your question can be answered by only one of these, try to rewrite your question so that it requires both. Note that "flipping" a word in the question can give rise to a new question where the answer will be different from the original question. Often, "flipping" a word gives rise to flipping the direction of the relationship, for example, from "increase" to "decrease."

Background Paragraph: A After a rock forms, nuclei of a radioisotope inside the rock start to decay. As they decay, the amount of the original, or parent, isotope decreases, while the amount of its stable decay product, or daughter isotope, increases. By measuring the relative amounts of parent and daughter isotopes and knowing the rate of decay, scientists can determine how long the parent isotope has been decaying. This provides an estimate of the rock's age.
Story: Gregory is a geologist who went on an excursion to Australia. While hiking in a cave, Gregory found two radioactive rocks containing Uranium. Gregory then brought the rocks back to his lab in Germany to conduct tests. Gregory discovered that rock A had high amounts of the original uranium isotope present, and low amounts of the daughter uranium isotope present. In rock B, however, there were low amounts of the original uranium isotope present and high amounts of the daughter uranium isotope present.
Which rock, rock A or rock B, had been decaying over a longer period of time?