[Solved] Biological oxidation-reduction reactions always involve: A) direct participation of oxygen. B) formation of water. C) mitochondria. D) transfer of electron(s). E) transfer of hydrogens. Sexual Behavior: Actions that individuals engage in to express their sexuality, including physical intimacy and erotic activities. Survey Research Method: A systematic collection of data from individuals using questionnaires or interviews to study and analyze opinions or behaviors. Casual Sex: Sexual activities occurring outside of a formal relationship without the expectation of commitment or emotional attachment. Observational Research: Studies in which the researcher unobtrusively observes people’s behavior and records the findings.