As far as I know, The correct answer is B. Fraternal twins are less similar than identical twins, demonstrating the impact of environmental factors.
Twin studies are used to investigate the relative contributions of genetic and environmental factors to various traits, such as intelligence, personality, and mental illness. In twin studies, researchers compare the similarities and differences in traits between identical (monozygotic) twins, who share 100% of their genes, and fraternal (dizygotic) twins, who share on average 50% of their genes, like any siblings.
If the trait is highly heritable, then identical twins should be more similar to each other than fraternal twins. If environmental factors have a greater influence, then fraternal twins should be more similar to each other than identical twins.
Studies have consistently found that identical twins are more similar to each other than fraternal twins for a variety of traits, indicating the strong influence of genetic factors. However, the degree of similarity between identical twins can vary depending on the trait, suggesting that environmental factors also play a role.
Moreover, fraternal twins are less similar to each other than identical twins, indicating the influence of environmental factors. Therefore, option B is the correct answer.