B. Formal operational stage of cognitive development
There can be a lot of factors that express sexuality. The origin would be its genes. The genetic make-up of the person what trait has passed on to an individual from his parents. Another factor is the environment. A person's sexuality can be influenced by social groups, home environment and from the media that he/she looks at.
B: receptor, sensory, interneuron, motor, effector
Yes, the story surprised me very much. However, I don’t think these similarities are something the twins inherited, I think they are coincidences. You can’t inherit the same wife or other similarity that are not decided by genes.