Select the option that can be used as a one-word substitute for the given group of words.
Indifferent to pleasure and pain

The correct answer is Stoic.

Let's analyze the meaning of the given phrase and compare it with the options to find the correct one-word substitute:
• Given phrase: "Indifferent to pleasure and pain" describes a person who can endure pain or hardship without showing their feelings or complaining, and remains unaffected by pleasure.
• Stoic: A person who can endure pain or hardship without showing their feelings or complaining. This term originates from Stoicism, an ancient Greek school of philosophy that teaches the development of self-control and fortitude as a means of overcoming destructive emotions. Thus, it is the perfect match.
• Cynic: A person who believes that people are motivated purely by self-interest rather than acting for honorable or unselfish reasons.
• Prudent: Acting with or showing care and thought for the future; wise or sensible.
• Lusty: Healthy, strong, and full of vigor or energy.

Therefore, the correct one-word substitute for "Indifferent to pleasure and pain" is Stoic.