Given the task definition and input, reply with output. 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.

Recent studies have shown that infectivity of the cytomegalovirus may require this functional group in its free form. It can be qualitatively detected using lead(II) acetate, which produces a yellow solid if this functional group is present. They are oxidized by mild oxidizing agents such as molecular iodine to produce disulfides, and cysteine is unique in that it is the only amino acid to bear this functional group. FTP, identify this functional group from organic chemistry formerly known as mercaptan and consisting of a sulfur atom bonded to a hydrogen atom.
Science