 You are given a background paragraph that describes one or more causal or physical relationships, such as a relationship in economics, scientific law, or nature. You need to come up with a fictional story that makes use of the concepts or the relationship described in the provided paragraph. Make sure that your story does not repeat the relation in the given paragraph (e.g., by avoiding verbatim copies of the given paragraph). Start by reading the background paragraph, and determine what relationship(s) are in the paragraph. Write a story that involves the relationship(s) that you determined are in the background paragraph. Try to use your own words as much as possible and not repeat the background paragraph. Feel free to make up places and events as long as they tie back to the background paragraph in a way that you can ask a question about.

Background Paragraph: Of the 94 naturally occurring elements, those with atomic numbers 1 through 82 each have at least one stable isotope (except for technetium, element 43 and promethium, element 61, which have no stable isotopes). Isotopes considered stable are those for which no radioactive decay has yet been observed. Elements with atomic numbers 83 through 94 are unstable to the point that radioactive decay of all isotopes can be detected. Some of these elements, notably bismuth (atomic number 83), thorium (atomic number 90), and uranium (atomic number 92), have one or more isotopes with half-lives long enough to survive as remnants of the explosive stellar nucleosynthesis that produced the heavy metals before the formation of our Solar System. At over 1.9×1019 years, over a billion times longer than the current estimated age of the universe, bismuth-209 (atomic number 83) has the longest known alpha decay half-life of any naturally occurring element, and is almost always considered on par with the 80 stable elements. The very heaviest elements (those beyond plutonium, element 94) undergo radioactive decay with half-lives so short that they are not found in nature and must be synthesized.
David was studying for his chemistry exam. To understand the elements of the periodic table better he categorized them into three groups, cat A, cat B, and cat C. In cat A he placed all the elements with atomic numbers lower than 83. In cat B he put the elements with atomic numbers from 83 to 94. Finally, in cat C he placed the elements with atomic numbers over 94. He found it easier to see their differences after he categorized them.