Definition: In this task you will be given a text passage from a trivia quiz. You should choose the category this question belongs to from these categories: History, Science, Social Science, Fine Arts, Literature. You can only choose one category, so if in doubt, please choose the closest match.
Input: Photolysis or pyrolysis in which a bond is broken without forming ions can produce these by-products of normal metabolism, which play a valuable role in fighting infection. Dr. Denham Harman, a professor emeritus at the University of Nebraska, is considered the father of a theory of aging in which they are key. Their namesake reactions involve covalent single bond changes in which one electron comes from each reactant. FTP, name these molecules with at least one unpaired valence electron, and thus an electrical charge, which can damage cell membranes and cause DNA mutations.
Output:
Science