A nurse is explaining the purpose of twin studies to a group of nursing students. Which of the following best describes what twin studies are designed to assess?

A. How birth order affects psychological outcomes in fraternal twins: Twin studies do not focus on birth order effects. While birth order may influence personality or behavior, this is outside the primary scope of twin research, which compares genetic and environmental contributions. B. The effectiveness of therapy interventions between different sibling groups: Twin studies are observational and designed to assess trait heritability, not therapeutic outcomes. They do not evaluate the impact of interventions between sibling groups. C. Whether shared environmental factors predict identical behaviors in all twins: Although shared environments are considered in twin studies, the goal is not to predict identical behaviors but to differentiate genetic influence from environmental influence. D. The influence of genetics versus environment on the development of traits or behaviors: Twin studies compare monozygotic (identical) and dizygotic (fraternal) twins to determine the relative contributions of heredity and environment to specific traits or behaviors. This method helps researchers estimate the heritability of psychological, behavioral, and physical characteristics.