Key rate duration (or partial duration) measures a bond's sensitivity to changes in the benchmark yield curve at specific maturity segments. Unlike effective duration, key rate durations help identify 'shaping risk,' which refers to a bond's sensitivity to changes in the shape of the benchmark yield curve (e.g., the curve becoming steeper or flatter). This makes option C the correct answer. Options A and B are incorrect because modified duration measures sensitivity to yield-to-maturity changes, and yield-to-worst is not directly related to key rate duration.