Explanation

Key rate duration is the most appropriate measure when an investor expects yield curve steepening because:

• Key rate duration measures the sensitivity of a bond's price to changes in yields at specific maturities along the yield curve
• Yield curve steepening means different parts of the yield curve are moving by different amounts (typically short-term rates remain stable while long-term rates rise)
• Effective duration assumes a parallel shift in the yield curve, which doesn't capture non-parallel movements
• One-sided duration focuses on asymmetric price changes but doesn't specifically address yield curve shape changes

Key rate duration allows investors to analyze how different segments of the yield curve will affect bond prices, making it ideal for analyzing steepening or flattening scenarios.