Concept:Triangulation in research means using multiple sources, methods, or theories to cross-check findings and improve validity.Explanation:Triangulation is most commonly used in qualitative research. It helps verify data and reduce bias. Researchers can use different data sources, investigators, theories, or methods (e.g., combining qualitative and quantitative approaches). This approach increases the credibility and depth of understanding of a research problem. It is especially valuable in qualitative research because it strengthens the interpretation of complex social or human phenomena. Although triangulation can appear in other research types, it originates and is primarily associated with qualitative methodology. Therefore, among the given options, triangulation is a method adopted by qualitative research.Answer:A. Qualitative Research