To strengthen the argument most effectively, claims C and D would be the best choices.
C presents a historical context about the origins of the UFC, highlighting the lack of regulations that permitted dangerous actions, which emphasizes the need for regulation to ensure fighter safety.
D discusses the reforms that were driven by public outcry and the need for improved safety and fairness, showing that regulation was not only necessary due to ethical concerns but also for the sustainability of the sport.
Together, these claims provide a solid foundation for arguing that regulation is essential for the safety and legitimacy of mixed martial arts.