Final answer:
The term 'antithesis' refers to someone or something that is the direct opposite of another person or thing. In the context of the question, Duane and his brother are opposites in both their social behaviors and interests.
Step-by-step explanation:
The phrase 'Duane is the antithesis of his brother' means that Duane exhibits qualities or characteristics that are directly opposite to those of his brother. For instance, if Duane is very shy, and in contrast, his brother is outgoing, this shows a clear discrepancy in their social behaviors. Furthermore, Duane's preference for reading over sports, which his brother favors, further highlights their contrasting interests and personalities.