Isaac,a 25-year-old law student,is heterosexual; his brother Chaim,a 21-year-old college senior,is homosexual. The brothers obviously differ in their

A) erotic plasticity.
B) sexual response cycle.
C) sexual orientation.
D) refractory period.

The brothers differ in their sexual orientation, with Isaac identifying as heterosexual and Chaim identifying as homosexual. Erotic plasticity refers to the degree to which an individual's sexuality can change over time or be influenced by social and environmental factors, and it is not necessarily related to one's sexual orientation. The sexual response cycle and refractory period refer to physiological responses during sexual activity and are not related to sexual orientation.