Explanation:

• Option A is incorrect because the GIPS standards mandate that non-discretionary portfolios must not be included in a firm's composites.
• Option B is incorrect because the GIPS standards prohibit firms from using phrases like "in accordance with," "in compliance with," or "consistent with" the GIPS standards when referring to their performance calculation methodology.
• Option C is correct because the GIPS standards allow a firm to determine a portfolio as non-discretionary if documented client-imposed restrictions significantly impede the implementation of the intended strategy, rendering the portfolio unrepresentative of the strategy.

This aligns with the ethical and professional standards, which outline the fundamentals of compliance, including the firm's definition of discretion.