Step 1: Understanding Stoicism.
Stoicism is a school of philosophy founded in Athens by Zeno of Citium. It emphasizes rationality, self-control, and virtue. Key figures in Stoicism include:
- A. Seneca: A Stoic philosopher, known for his writings on ethics.
- B. Marcus Aurelius: A Roman Emperor and Stoic philosopher, who wrote Meditations on Stoic philosophy.
- C. Epictetus: A former slave who became a famous Stoic philosopher.
- D. Protagoras: A pre-Socratic philosopher, but not associated with Stoicism; he was more aligned with relativism.
Step 2: Conclusion.
The correct answer is 3. A, B, C only.
Final Answer:
\[
\boxed{\text{The correct answer is 3. A, B, C only.}}
\]