Explanation

Let's analyze each statement:

A. Not all risk is diversifiable. - This is accurate. Total risk consists of systematic risk (market risk) and unsystematic risk (specific risk). Systematic risk cannot be diversified away.

B. Unsystematic risk can be substantially reduced by diversification. - This is accurate. Unsystematic risk, also known as specific risk or idiosyncratic risk, can be significantly reduced through proper diversification across different securities and industries.

C. Systematic risk can be eliminated by holding securities in a well-diversified international stock portfolio. - This is least accurate. Systematic risk (market risk) affects all securities in the market and cannot be eliminated through diversification, even with international diversification. International diversification can reduce country-specific risks but cannot eliminate global systematic risk factors.

D. None of above. - This is incorrect since option C is inaccurate.

Therefore, option C is the least accurate statement because systematic risk cannot be eliminated through diversification, regardless of how well-diversified the portfolio is.